The biotransformation of isosafrole by Cladosporium sphaerospermum yielded piperonal, which is a compound of great commercial importance in the flavor and fragrance industries. The experiments were performed in 500-mL conical flasks containing 100 mL of Czapek-modified medium in an orbital shaker with controlled agitation and temperature. Spores of C. sphaerospermum were used as inocula, and after 96 h of incubation the substrate was added to the culture. Samples of 2 mL were withdrawn at 24-h intervals and analyzed by gas chromatography, (GC) and/or GC/MS spectroscopy.