A sensitive gas chromatographic method for the determination of the quinoline alkaloid viridicatin, a fungal metabolite isolated from several Penicillium species and presumably a biogenetic precursor to naturally occurring diazepam-like 1,4-benzo-diazepines, has been developed. Prior to conversion of viridicatin into a volatile trimethylsilyl derivative, a rapid sample clean-up was accomplished by solid-phase extraction from mould mycelium on a C18 cartridge. Using synthetical 6-bromo-viridicatin as an internal standard, the amount of viridicatin produced de novo in emerged grown cultures of Penicillium cyclopium strain SM 72 was calculated in correlation to the duration of mould cultivation.