Since 1987, the brown ring disease has caused mass mortalities on cultured clam-beds on the west coast of France. Our objective was to establish the MIC (minimal inhibitory concentration), the in vivo toxicity and effectiveness of several antiseptic and antibiotic agents, in order to obtain useful information for farmers in controlling epizootics. Among the different drugs tested, furazolidone was the most efficient in the control of this clam disease. Administration of 10 mg/l for 3 days (every day, infected clams were left in filtered (1 μm), sterilized, new, static sea-water supplemented with the determined furazolidone dose) seemed to give 100% protection against the Vibrio. © 1992.