Three new natural mycotoxins, analogues of ochratoxin A, in which the phenylalanine moiety is replaced by serine, hydroxyproline or lysine, were isolated from cultures of Aspergillus ochraceus by TLC followed by HPLC column chromatography. Their structures were determined after acidic hydrolysis by the characterisation of both their amino acid moieties and of ochratoxin alpha, the chlorinated dihydroisocoumarin moiety of ochratoxin A. These structures were confirmed by mass spectrum analysis.