This study examines the anti-ulcerogenic activity of a chloroform extract of Tanacetum vulgare and purified parthenolide, the major sesquiterpene lactone found in the extract. Gastric ulcers induced by oral administration of absolute ethanol to rats were reduced dose-dependently by oral pretreatment of animals with the chloroform extract (2.5-80 mg kg(-1)) or parthenolide (5-40 mg kg(-1)). When administered 30 min before challenge with the alcohol the protection ranged between 34 and 100% for the extract and 27 and 100% for parthenolide. When the products were administered orally 24 h before treatment with ethanol, 40 mg kg(-1) of the extract and of the lactone reduced the mean ulcer index from 4.8+/-0.3 for control animals to 1.4+/-0.2 and 0.5+/-0.1, respectively. The products also prevented alcohol-induced reduction of the number of sulphydryl groups within the gastric mucosa (50.6+/-2.3 microg (mgprotein)(-1) for normal animals compared with 17.7+/-3.0 microg (mg protein)(-1) for alcohol-treated animals). Administration of the extract (80 mg kg(-1)) or parthenolide (40 mg kg(-1)) 24 h before ethanol treatment restored the numbers of mucosal -SH groups to values near those found for normal animals. These results suggest that the products assayed, in particular parthenolide, might find therapeutic application, although further work is required to establish their profit/risk ratio.