The safety of bacterial cells of Clostridium bifermentans serovar malaysia, which is highly toxic to mosquito larvae, was tested on mice, guinea pigs, rabbits, and goldfish. Inoculations of at least 1 x 10(8) cells per animal by routes recommended by World Health Organization (subcutaneous, percutaneous, inhalation, force-feeding, intraperitoneal, intravenous) and tests of subacute toxicity, anaphylactic shock, persistence in heart blood, and virulence by successive passages, were performed on mice, guinea pigs, or both. Growth was monitored for 1 mo before necropsy. Ocular irritation and skin scarification were tested with rabbits. C. bifermentans serovar malaysia did not induce any mortality or abnormal reactions in mammals at a dose 1,000 times higher than the level established by W.H.O. for the demonstration of safety. Bacterial cells are not toxic to goldfish at a dose 1,000 times higher than the LD50 for the target-mosquito larvae. We conclude that C. bifermentans serovar malaysia bacterial cells are safe for laboratory mammals and goldfish.