Twenty metabolites, citreohybridones, have been isolated from the mycelium of the hybrid strain KO 0031, prepared by cell fusion technique using Penicillium citreo-viride B. IFO 6200 and 4692. Their stereostructures have been elucidated on the basis of their spectral data and some chemical evidence, and their absolute configurations have been also elucidated by the modified Mosher's methods. Incorporation of 13 C-labelled acetate, formate and ethyl 3,5-dimethylorsellinate into citreohybridones has established that their biosynthesis proceeds via a mixed polyketide-terpenoid (meroterpenoid) pathway.