The gastroprotective effect of the labdane diterpene solidagenone was assessed on gastric ulcer in rats. The effect of a single oral dose of the compound was evaluated at 50, 100 and 200 mg kg(-1) in the following test systems: pylorus ligature (Shay), aspirin- and ethanol-induced gastric ulcers. In pylorus-ligated rats (Shay model), the ulcerative index decreased by 37% with solidagenone pre-treatment at the three assayed doses. The effect of a single oral dose of 50 mg kg(-1) solidagenone was comparable with ranitidine at the same concentration and similar to higher doses of the compound. A significant effect (P < 0.001) at 100 and 200 mg kg(-1) was observed in the aspirin-induced ulcer model. At both doses, reduction in the number of lesions was approximately 50% compared with controls. The effect was comparable with the reference compound ranitidine (50 mg kg(-1)). With the ethanol-induced gastric ulcers, the effect of solidagenone at 100 and 200 mg kg(-1) was similar to a single oral dose of 20 mg kg(-1) omeprazole with a 50% reduction of the mean number of lesions compared with controls. In acute toxicity tests on mice, intraperitoneal administration of solidagenone showed no toxicity at doses up to 600 mg kg(-1). This is the first report on the gastroprotective activity of a labdane diterpene.