question: The toxicity of an isolate of Aspergillus ochraceus was examined in weanling male Sprague-Dawley rats fed diets containing a rice culture or fungal mat of the organism for 5 wk. The ground rice culture was mixed with a commercial purified diet at concentrations of 5, 7·5 and 10% and the fungal mat at concentrations of 1, 2 and 3%. In groups fed the rice-culture diets, weight gains were reduced and all the rats in the group fed the 10% diet died. Rats fed fungal-mat diets showed a marked reduction in weight gain, and the death rate was high (about 83%) in groups fed the 2 or 3% diet. Gross lesions found in groups fed either type of diet included focal necrosis in the liver, greenish discoloration of the kidneys, gastric ulceration, ulceration of the scrotal epidermis and corneal opacity. Histological changes in the liver included necrosis of the epithelium of biliary ducts, periductal oedema, pericholangitis, periductal fibrosis and disseminated focal hepatocellular necrosis. Necrosis of epithelium occurred also in the extraheptic ducts and was accompanied by an interstitial pancreatitis in certain rats. Foci of leucocytes and macrophages were found in the dermis of the scrotum and in the epididymal adipose connective tissue. Ulceration of the epidermis occurred late in the sequence of scrotal changes. Ocular lesions comprised corneal oedema, interstitital keratitis, iridocyclitis and hypopyon. Renal lesions consisted of tubular necrosis and hyaline and biliary casts within convoluted tubules.