Dehydroabietic acid derivatives have been reported to display antisecretory and antipepsin effect in animal models. Some 19 dehydroabietic acid diterpenes were prepared and assessed for gastroprotective activity in the HCl/EtOH-induced gastric lesions in mice as well as for cytotoxicity in human lung fibroblasts (MRC-5) and human epithelial gastric (AGS) cells. At a single oral dose of 100 mg kg(-1), highest gastroprotective effect was provided by dehydroabietanol, its corresponding aldehyde, dehydroabietic acid (DHA) and its methyl ester, N-(m-nitrophenyl)-, N-(o-chlorophenyl)- and N-(p-iodophenyl)abieta-8,11,13-trien-18-amide (compounds 12-14), N-2-aminothiazolyl- and N-benzylabieta-8,11,13-trien-18-amide (compounds 18-19) being as active as lansoprazole at 20 mg kg(-1) and reducing the lesion index by at least 75%. In the compound series including the alcohol, ester, aldehyde, acid and methyl ester at C-18 (compounds 1-9), highest activity was related with the presence of an alcohol, aldehyde, acid or methyl ester at C-18, the activity being strongly reduced after esterification. The cytotoxicity of the compounds 1-9 towards AGS cells and fibroblasts was higher than the values for the amides 10-19. In the compounds 10-19, the best gastroprotective effect was observed for the aromatic amides 12-14 (75-85% inhibition of gastric lesions) bearing a nitro or halogen function in the N-benzoyl moiety. Lowest cytotoxicity was found for the amides, with IC(50) values >1000 microM for fibroblasts and from 200 up to >1000 microM for AGS cells, respectively. The N-2-aminothiazolyl- and N-benzylamide derivatives were also very active as gastroprotectors with higher cytotoxicity against AGS cells.