Abiesenonic acid methyl ester (AVB-I acid methyl ester), a triterpenoid compound prepared from abieslactone, suppressed tumor promoter-induced phenomena in vitro and in vivo; i.e., AVB-I acid methyl ester inhibited 12-o-tetradecanoylphorbol-13-acetate (TPA)-stimulated 32Pi-incorporation into phospholipids of cultured cells and the promoting action of TPA on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene.