A carcinogenic mycotoxin that is primarily produced by Aspergillus versicolor and Aspergillus nidulans, although other molds (e.g., Aspergillus flavus, Aspergillus rugulosus, Bipolaris spp., Penicillium luteum) are also capable of producing sterigmatocystin. Sterigmatocystin is structurally related to the aflatoxins and is equally stable. It is a potent hepatotoxin causing bile duct hyperplasia in ducklings and hyperplasia of the hepatocytes with little bile duct proliferation and liver necrosis in rats. Factors involved in fungal growth and toxin production include lactose, fat, and some fat hydrolysis products. Occurrence of sterigmatocystin has been reported in grains and the outer layer of hard cheeses when these have been colonized by Aspergillus versicolor.