The studies reported represent the preclinical toxicologic evaluation of bumetanide. Toxicity testing in rats, rabbits, dogs, and baboons indicate that bumetanide is well tolerated in various species. The toxicity that was observed is, for the most part, the direct consequence of its potent diuretic activity and is similar to that produced by other "loop" diuretics. Bumetanide was fetotoxic at maternal toxic doses in the rabbit, but no evidence of teratogenic effects was observed in rabbits, rats, mice, or hamsters. The compound was devoid of mutagenic activity by the Ames test and was found to be noncarcinogenic in long-term rat studies.