8-K

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549




                                    FORM 8-K



                                 CURRENT REPORT


     Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934



          Date of Report (date of earliest event reported): May 3, 1999



                           MOLECULAR BIOSYSTEMS, INC.
             (Exact name of registrant as specified in its charter)



                          Delaware 1-10546 36-30878632
              (State or other juris- (Commission file (IRS employer
            diction of incorporation) number) identification number)



              10030 Barnes Canyon Road, San Diego, California 92121
                    (Address of principal executive offices)



       Registrant's telephone number, including area code: (619) 812-7200







Item 5. Other Events.

     Molecular Biosystems, Inc. and Mallinckrodt, Inc. Receive Notice of Lawsuit

         On May 5, 1999, Molecular Biosystems, Inc. (the "Company") announced
that DuPont Pharmaceuticals Company ("DuPont") and ImaRx Pharmaceutical Corp. 
("ImaRx") filed a lawsuit in the United States District Court for the District
of Delaware against MBI and its marketing partner Mallinckrodt, Inc.  The 
lawsuit alleges that the manufacture and sale of OPTISON(r) infringes 
U.S. Patent No. 5,547,656 owned by ImaRx and exclusively licensed to DuPont.

         A copy of the press release that the Company jointly issued with 
Mallinckrodt, Inc., on May 5, 1999, is attached to this Report as Exhibit 99.1.
Mallinckrodt, Inc., is the Company's marketing partner for OPTISON in the
United States and most other regions of the world.

         Statements in this current report on Form 8-K may constitute forward 
looking statements and are subject to numerous risks and uncertainties.  Among
the factors that could result in a materially different outcome are:  the 
failure of OPTISON to gain market acceptance either in the U.S. or other 
markets; an adverse result in MBI's and Mallinckrodt's pending patent lawsuits,
including the lawsuit announced by DuPont and ImaRx, or an adverse ruling by 
the PTO in the pending patent reexaminations; and other risk factors reported
from time to time in MBI's and Mallinckrodt's filings with the Securities and 
Exchange Commission.


                                    Signature
      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 hereunto duly authorized.

           Date:   May 12, 1999


           Molecular Biosystems, Inc.



           By      /s/ Elizabeth L. Hougen
                      Elizabeth L. Hougen
                  Executive Director, Finance and Chief Financial Officer




                                  Exhibit Index

Sequentially
 Exhibit              Description                          Numbered Page

  99.1                Press release (May 5, 1999)                5

EX-99.1

                                                                  Exhibit 99.1

FOR IMMEDIATE RELEASE

Molecular Biosystems Contacts:
Elizabeth Hougen, Chief Financial Officer (619) 812-7179
Patricia Sullivan, Manager, Investor Relations (619) 812-7146


Mallinckrodt Contacts:
Media Contact:  Barbara Abbett, (314) 654-5230
       E-mail:  Communications@mkg.com

Investor Contact:  Barbara Gould, (314) 654-3190
                   Invest@mkg.com


                 MBI and Mallinckrodt Receive Notice of Lawsuit

San Diego, California  and St. Louis, Missouri, May 5, 1999 - Molecular
Biosystems, Inc. (NYSE: MB) and Mallinckrodt Inc. (NYSE: MKG) said today that 
the two companies will aggressively defend their rights to manufacture and sell
OPTISON(r), the only advanced generation cardiac ultrasound imaging agent
commercially available in the United States and Europe.

The announcement was made after DuPont Pharmaceuticals Company ("DuPont") and 
ImaRx Pharmaceutical Corp. ("ImaRx") filed a lawsuit in the United States 
District Court for the District of Delaware against MBI and its marketing
partner Mallinckrodt.  The lawsuit alleges that the manufacture and sale of
OPTISON infringes U.S. Patent No. 5,547,656 owned by ImaRx and exclusively 
licensed to DuPont.

"MBI firmly believes that the patent is invalid and the manufacture and sale of
OPTISON does not infringe this patent," stated MBI's President and CEO Bobba 
Venkatadri.  He further stated, "We will take all actions necessary to preserve
MBI's and Mallinckrodt's right to manufacture and sell OPTISON." Bradley J. 
Fercho, president of Mallinckrodt's Imaging Group, said that the two companies
expect to vigorously defend against the legal actions being pursued by their
competitors.

Developed by MBI and marketed in the United States and Europe by Mallinckrodt, 
OPTISON is used in more than 1,600 hospitals and cardiology group practices in 
the United States, Germany, Spain and the United Kingdom.  MBI holds more than 
60 valid patents worldwide protecting its proprietary microsphere technology, 
which has enabled the development of OPTISON.

MBI, based in San Diego, California, is a world leader in developing contrast
agents for diagnostic imaging.  Its innovative product, OPTISON, enables 
improved diagnosis of heart disease through clearer ultrasound images.

Based in St. Louis, Missouri, Mallinckrodt has three healthcare product groups -
Imaging, Pharmaceuticals and Respiratory.  It operates in more than 100 
countries and had fiscal 1998 sales of $2.4 billion.

This news release contains forward-looking statements that involve risks and
uncertainties.  Among the factors that could result in a materially different
outcome are:  the failure of OPTISON to gain market acceptance either in the
U.S. or other markets; an adverse result in MBI's and Mallinckrodt's pending
patent lawsuits, including the lawsuit announced by DuPont and ImaRx, or an 
adverse ruling by the PTO in the pending patent reexaminations; and other risk
factors reported from time to time in MBI's and Mallinckrodt's filings with the
Securities and Exchange Commission.



   For More Information on Molecular Biosystems by Fax, Dial 888-329-4007, or
Visit its Website: www.mobi.com

For More Information on Mallinckrodt, Visit its Website: www.mallinckrodt.com