Fumonisin B1 is hepatotoxic in all species, but nephrotoxicity has only been reported in rats. It is a specific inhibitor of sphinganine N-acyltransferase. Our objective was to determine the target organs for fumonisin toxicosis in the rabbit. We administered fumonisin B1 ( > 95% pure) intravenously to adult rabbits and examined selected clinical, biochemical, and histological parameters for up to 5 days. In a pilot study, rabbits were given fumonisin B1 at 1, 0.5, 0.3, 0.15, or 0 mg/kg daily for 4 or 5 days and then euthanized. Additional rabbits were given a single dose of fumonisin B1 at 1 mg/kg and euthanized on day 2 or 4. In the formal time-course study, rabbits were given a single dose of fumonisin B1 at 0 or 1.25 mg/kg and euthanized on days 1, 3, or 5. Rabbits given multiple doses of fumonisin B1 were lethargic and anorectic, and had decreased urine production. Liver- and renal-associated clinical chemistry parameters were elevated. Renal lesions consisted of severe proximal tubular necrosis. Liver lesions were variable and consisted of mild necrosis, hepatocyte vacuolation, and bile stasis. The sphinganine-to-sphingosine ratio, in both target and nontarget tissues, was markedly elevated in treated rabbits. A single dose of fumonisin B1 induced renal but not hepatic injury. Therefore, the target organs for fumonisin B1 toxicity in rabbits are kidney and liver, with the kidney being more sensitive.