SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                    --------

                                    FORM 6-K

                        REPORT OF FOREIGN PRIVATE ISSUER
                      PURSUANT TO RULE 13A-16 OR 15D-16 OF
                       THE SECURITIES EXCHANGE ACT OF 1934

                           For the month of May, 2005

                                   Serono S.A.
                -----------------------------------------------
                               (Registrant's Name)

                            15 bis, Chemin des Mines
                                 Case Postale 54
                                CH-1211 Geneva 20
                                   Switzerland
                    ---------------------------------------
                    (Address of Principal Executive Offices)

                                     1-15096
                            -------------------------
                              (Commission File No.)

     (Indicate by check mark whether the registrant files or will file annual
reports under cover of Form 20-F or Form 40-F.)

     Form 20-F  X  Form 40-F
               ---          ----

     (Indicate by check mark if the registrant is submitting the Form 6-K in
paper as permitted by Regulation S-T Rule 101 (b)(1).)
                                                      ------

     (Indicate by check mark if the registrant is submitting the Form 6-K in
paper as permitted by Regulation S-T Rule 101 (b)(7).)
                                                       -------

     (Indicate by check mark whether the registrant by furnishing the
information contained in this form is also thereby furnishing the information to
the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of
1934.)

     Yes      No  X
         ----    ----

     (If "Yes" is marked, indicate below the file number assigned to the
registrant in connection with Rule 12g3-2(b): 82-       )
                                                 ------



[GRAPHIC OMITED]
SERONO                                                                  BIOMARIN



MEDIA RELEASE

FOR IMMEDIATE RELEASE
---------------------


                 BIOMARIN AND SERONO FORM STRATEGIC ALLIANCE FOR
    THE DEVELOPMENT AND COMMERCIALIZATION OF PHENOPTIN(TM) AND PHENYLASE(TM)

                      PHENOPTIN CURRENTLY IN PHASE 3 TRIALS

NOVATO,  CALIFORNIA,  AND  GENEVA,  SWITZERLAND,  MAY  16,  2005  -  BioMarin
Pharmaceutical  Inc.  (Nasdaq  and  SWX: BMRN) and Serono (virt-x: SEO and NYSE:
SRA)  announced today that they have formed a strategic alliance for the further
development  and commercialization of two BioMarin product candidates, Phenoptin
(sapropterin  hydrochloride)  and  Phenylase (phenylalanine ammonia lyase). Both
products  have  shown  potential  in the treatment of phenylketonuria (PKU), and
there  is preliminary clinical evidence that suggests that the active ingredient
in  Phenoptin,  a  synthetic  form  of  the  naturally occurring enzyme cofactor
6R-BH4, may also be useful in the treatment of other serious diseases, including
diabetes  and  cardiovascular  diseases.

By  the terms of their agreement, Serono acquires exclusive rights to market the
products  in  all  territories  outside  the  United  States and Japan. BioMarin
retains  exclusive  rights  to  market the products in the United States. Serono
will  make  an  upfront  payment  of  $25  million  to  BioMarin,  and will make
additional  milestone  payments  of  up  to $232 million based on the successful
development  and registration of both products in multiple indications, of which
$45  million are associated specifically with Phenoptin in PKU. Serono will also
pay  BioMarin  undisclosed  royalties  on  its  net  sales  of the products. The
companies  will  share  equally  all  development  costs  following  successful
completion  of  Phase  2  trials  for each product candidate in each indication.

BioMarin  is  currently investigating Phenoptin, an orally administered product,
in  a  Phase  3  clinical  trial  for  the treatment of PKU. PKU is an inherited
metabolic  disease  caused  by  a  deficiency  of  the  enzyme  phenylalanine
hydroxylase,  resulting  in elevated levels of phenylalanine in the blood, which
can  result  in serious neurological damage. There is currently no approved drug
to  treat PKU, which affects at least 50,000 diagnosed patients under the age of
40  worldwide.  Phenylase,  an  enzyme substitution therapy for the treatment of
severe  forms  of  PKU,  is  currently  in  preclinical  development.

Emil  Kakkis  MD,  PhD, Senior Vice President of Business Operations at BioMarin
commented,  "We  are  very pleased to enter into this partnership with Serono, a
top-tier  biotechnology  company with strong global development capabilities and
commercial  operations.  Serono's  expertise  in  developing and marketing novel
products for metabolic and genetic diseases will be an invaluable asset for this
partnership."

"We  are  delighted  to  partner  with  BioMarin for the further development and
commercialization of Phenoptin and Phenylase, products that fit very nicely into
our  metabolic  endocrinology franchise," said Franck Latrille, Senior Executive
Vice  President  Global  Product  Development  at  Serono.  "PKU  is  a severely
debilitating  condition  afflicting  patients  from  birth  and throughout their
lives.  Serono's strategy is to invest in bringing to market innovative products
like  Phenoptin  and  Phenylase  that  address significant unmet medical needs."


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ABOUT  BIOMARIN
BioMarin  develops  and commercializes innovative biopharmaceuticals for serious
diseases and medical conditions. The company's product portfolio is comprised of
two  approved  products,  Aldurazyme(R) (laronidase) for mucopolysaccharidosis I
(MPS I), and Orapred(R) (prednisolone sodium phosphate oral solution) for severe
asthma,  and  multiple  product  candidates  including  rhASB  (galsulfase),  a
BLA/MAA-stage  product  candidate  for the treatment of mucopolysaccharidosis VI
(MPS  VI),  and  Phenoptin(TM)  (sapropterin  hydrochloride),  a Phase 3 product
candidate  for  the  treatment  of  phenylketonuria  (PKU).  For  additional
information,  please  visit  www.BMRN.com.  Information on BioMarin's website is
                             ------------
not  incorporated  by  reference  into  this  press  release.

ABOUT  SERONO
Serono  is  a  global  biotechnology leader. The Company has eight biotechnology
products,  Rebif(R),  Gonal-f(R),  Luveris(R),  Ovidrel(R)/Ovitrelle(R),
Serostim(R),  Saizen(R),  Zorbtive(TM)  and Raptiva(R). In addition to being the
world  leader  in  reproductive  health,  Serono  has strong market positions in
neurology,  metabolism  and  growth and has recently entered the psoriasis area.
The  Company's  research programs are focused on growing these businesses and on
establishing  new  therapeutic  areas, including oncology.  Currently, there are
approximately  30  ongoing  development  projects.

In  2004,  Serono  achieved  worldwide revenues of US$2,458.1 million, and a net
income  of  US$494.2 million, making it the third largest biotech company in the
world.  Its  products  are  sold  in over 90 countries.  Bearer shares of Serono
S.A.,  the  holding  company,  are  traded  on the virt-x (SEO) and its American
Depositary  Shares  are  traded  on  the  New  York  Stock  Exchange  (SRA).
                                      #####

FORWARD-LOOKING  STATEMENTS

FOR BIOMARIN
This  press  release  contains  forward-looking  statements  about  the business
prospects  of  BioMarin  Pharmaceutical  Inc.,  including,  without  limitation,
statements  about:  the  development  of  its  product  candidates Phenoptin and
Phenylase;  expectations  related  to  the  possible  use  of  Phenoptin for the
treatment of indications other than PKU; and the possible milestone revenue from
development  of  these  product candidates. These forward-looking statements are
predictions  and  involve  risks  and uncertainties such that actual results may
differ  materially from these statements. These risks and uncertainties include,
among  others:  the  results  of  preclinical  and  clinical  trials  related to
Phenoptin and Phenylase, both for the treatment of PKU and for indications other
than PKU; results and timing of current and planned clinical trials of Phenoptin
for  the  treatment of PKU; the content and timing of decisions by the U.S. Food
and  Drug  Administration,  the  European  Medicines Agency and other regulatory
authorities  concerning Phenoptin and Phenylase; the ability to develop suitable
formulations of Phenylase; the ability to develop commercial scale manufacturing
for  Phenoptin  and  Phenylase; and those factors detailed in BioMarin's filings
with  the Securities and Exchange Commission, including, without limitation, the
factors  contained under the caption "Factors That May Affect Future Results" in
BioMarin's  2004  Annual  Report  on  Form  10-K  and  the  factors contained in
BioMarin's  reports  on  Forms 10-Q and 8-K. Stockholders are urged not to place
undue  reliance  on  forward-looking statements, which speak only as of the date
hereof. BioMarin is under no obligation, and expressly disclaims any obligation,
to  update  or  alter  any  forward

FOR SERONO
Some  of  the  statements  in  this  press  release  are  forward  looking. Such
statements  are inherently subject to known and unknown risks, uncertainties and
other  factors  that  may  cause  actual results, performance or achievements of
Serono  S.A.  and  affiliates  to be materially different from those expected or
anticipated  in  the  forward-looking statements. Forward-looking statements are
based on Serono's current expectations and assumptions, which may be affected by
a  number  of  factors, including those discussed in this press release and more
fully  described  in  Serono's  Annual  Report  on Form 20-F filed with the U.S.
Securities  and Exchange Commission on March 16, 2005. These factors include any
failure  or  delay  in  Serono's ability to develop new products, any failure to
receive  anticipated  regulatory  approvals,  any  problems  in  commercializing
current  products  as  a  result of competition or other factors, our ability to
obtain  reimbursement  coverage  for  our  products,  the  outcome of government
investigations and litigation and government regulations limiting our ability to
sell  our  products.  Serono has no responsibility to update the forward-looking
statements  contained  in  this press release to reflect events or circumstances
occurring  after  the  date  of  this  press  release.


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                                      #####

Aldurazyme(R)  is  a  registered  trademark  of  BioMarin/Genzyme  LLC.
Orapred(R)  is  a  registered trademark of Medicis Pediatrics, Inc., and is used
under  license.

CONTACTS:

FOR BIOMARIN:

Investors                                        Media
Joshua  A.  Grass                                Susan  Ferris
BioMarin Pharmaceutical Inc.                     BioMarin Pharmaceutical Inc.
(415) 506-6777                                   (415) 506-6701
http://www.bmrn.com


FOR  SERONO:

  Corporate Media Relations:            Corporate Investor Relations:
  Tel:  +41  22  739  36  00            Tel:  +41  22  739  36  01
  Fax:  +41  22  739  30  85            Fax:  +41  22  739  30  22
  http://www.serono.com                 Reuters:  SEO.VX  /  SRA.N
  ---------------------                 Bloomberg:  SEO  VX  /  SRA  US

  Media  Relations,  USA:               Investor  Relations,  USA:
  Tel:  +1  781  681  2340              Tel:  +1  781  681  2552
  Fax:  +1  781  681  2935              Fax:  +1  781  681  2912
  http://www.seronousa.com
  ------------------------

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                                   SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned, thereunto duly authorized.



                                            SERONO S.A.
                                            a Swiss corporation
                                            (Registrant)



May 16, 2005                         By:    /s/ Stuart Grant
                                            ------------------------------
                                            Name: Stuart Grant
                                            Title: Chief Financial Officer