Technical Abstract: The fungus Fusarium moniliforme produces fumonisins, a class of mycotoxins found in corn-based feeds and foods worldwide and is suspected of being human esophageal carcinogens. Fumonisin B1, the most common homologue, causes equine leukoencephalomalacia and porcine pulmonary edema. It has cancer promoting activity, is hepatotoxic and nephrotoxic in various species, and disrupts sphingolipid metabolism in vivo. The in vivo effects of other fumonisins are, however, not defined. To determine if fumonisins B2 or B3 may contribute to fumonisin-related health risks, 6 groups of male rats (n=10/group) were fed diets containing low, mid, or high levels of culture materials made from F. moniliforme isolates which produced either fumonisin B2 (FB2CM) or B3 (FB3CM), but did not produce fumonisin B1. Three more groups were fed diets with low, mid, or high level of fumonisin B1 containing culture material (FB1CM). A tenth group was fed an untreated control diet. After three weeks (wk3), 5 rats per group were killed for microscopic tissue evaluations. The remainder were placed on an untreated control diet for 3 additional weeks and then killed (wk6) for histopathological studies. After wk3, toxicological and histopathological findings in the high level FB2CM and FB3CM groups were similar to those seen in the high level FB1CM group, were typical of those caused by F. moniliforme and fumonisin B1, and included decreased relative (organ/brain ratio) kidney weights, hepatopathy, and nephropathy. These effects were reversible. Except for mild focal cholangiofibrosis found in 3 high level FB1CM rats, no serum chemical, relative organ weight or histopathological effects were found in the FB2CM, FB3CM and FB1CM groups at wk6.