The antiulcer activity of a short-boiled aqueous extract from aerial parts of Cistus incanus was studied in rats against gastric lesions induced by necrotizing agents (1N HCl and absolute ethanol), indomethacin, serotonin and reserpine. The extract, containing bioflavonoids, was orally administered in the range from 0.25 to 0.50 g kg-1. It was found to have significant dose-related protective effects in all these experimental models, and was more effective against reserpine- and serotonin-induced mucosal congestion and haemorrhagic ulcers. These data suggest that the active constituents of the crude extract could be responsible for its protective effect by maintaining an efficient gastric mucosal microvascular supply.