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 23, 2000 MOLECULAR BIOSYSTEMS, INC. (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER) DELAWARE 1-10546 36-3078632 (STATE OF INCORPORATION) (COMMISSION FILE NUMBER) (I.R.S. IDENTIFICATION NO.) 10030 BARNES CANYON ROAD, SAN DIEGO, CALIFORNIA 92121 (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES) REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE: (858) 812-7001 Item 5. Other Events MOLECULAR BIOSYSTEMS, MALLINCKRODT ANNOUNCE RESTRUCTURING OF OPTISON AGREEMENT. On May 8, 2000, Molecular Biosystems, Inc. and Mallinckrodt Inc. announced the restructuring of their agreement concerning OPTISON. Under the terms of the agreement, Mallinckrodt will assume full control of the OPTISON business, including responsibility for intellectual property disputes, clinical development, manufacturing and real estate. In addition, a settlement was reached in three ongoing patent disputes in Washington, DC, Seattle, WA, and Europe between Nycomed, Mallinckrodt, Molecular Biosystems and SONUS Pharmaceuticals. Item 7. Financial Statements and Exhibits 10.1 Press release dated May 8, 2000 10.2 OPTISON Product Rights Agreement 10.3 Settlement Agreement 2 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. MOLECULAR BIOSYSTEMS, INC. /s/ BOBBA VENKATADRI - -------------------------------- Bobba Venkatadri President and Chief Executive Officer 5/23/00 - -------------------------------- Date 3 EXHIBIT INDEX Exhibit Description 10.1 Press release dated May 8, 2000 10.2 OPTISON Product Rights Agreement 10.3 Settlement Agreement 4