Ochratoxin A is a polyketide-derived dihydroiso-coumarin moiety linked through the 12-carboxy group to phenylalanine. Ochratoxin A is the most important and most commonly occurring of a structurally related group of compounds. It is produced by some species of Aspergillus, such as A. ochraceus, mainly in tropical regions, and by Penicillium verrucosum, a common storage fungus in temperate areas such as Canada, eastern and north western Europe and parts of South America. Ochratoxin A is a potent toxin affecting mainly the kidneys, in which it can cause both acute and chronic lesions, whereas its dechloro derivative, ochratoxin B, is non-toxic. A nephrotoxic effect has been demonstrated in all mammalian species.