Ethyldelta-gtetrahydrocPnnabinol (ethyldelta-8-THC) and ethyldelta-9-THC were synthesized by condensation of 5-ethyl-l,3dihydroxybenzene and lS-cis-verbenol. The two cannabiaoids were administered to male Charles River CD-1 mice and hepatic metabolites were extracted with ethyl acetate and isolated by chromatography on Sephadex LH-20. Metabolite identification was by gas chromatograpby/mass spectrometry as trimethylsilyl (TMS), ('H9)TMS, methyl esternMS and dihydroPMS derivatives. Metabolites from ethyldelta-&THC, of which six were identilied, were similar with respect to the positions substituted on the terpene ring to those produced by higher homologues; the major metabolite, accounting for about 95% of the metabolic fraction, was ethyldelta-STHC-1 l-oic acid. Side-chain hydroxy metabolites were not detected. Metabolism of ethyldelta-%THC was also similar to that of the higher homologues with the exception that less metabolism occurred at C-8 and a higher percentage of the total metabolic fraction was accounted for by the ll-oic acid metabolite. Five metabolites were identified; minor metabolites were mainly dihydroxylated compounds and hydroxylated derivatives of ethyl-delta-9-THC-11-oic acid. A dihydro-metabolite, the C-9-axial-COOH isomer of ethyl-hexahydrocannabinol-ll-oic acid, was produced by both compounds and a trace of ethyl-CBN-ll-oic acid was produced by ethyldelta-9-THC.