Differential display reverse transcription polymerase chain reaction experiments were performed to monitore Ochratoxin A biosynthetic genes inPenicillium verrucosum BFE487. A stringent prerequisite for the performance of this type of experiments is the knowledge of the differential expression of OTA genes. Differentially expressed total RNA from permissive/restrictive growth conditions and alternatively OTA(+) wild type/OTA mutant strains have been isolated, reverse transcribed and used as a template in DDRT-PCR experiments. About 70 differentially expressed cDNA fragments could be isolated, cloned and sequenced.