Investigations were carried out to determine the gastroprotective effects of the flavonoid fraction of Dittrichia viscosa (L.) W. Greuter against gastric lesions produced by necrotizing agents. The action of the fraction on the production of mucus, and the involvement of endogenous PGs in gastric mucosal defensive mechanisms were also determined. Gastric ulcers induced by oral administration of three necrotic agents (100% ethanol, 0.6 N HCl, 30% NaCl) were markedly reduced by pretreatment with the flavonoid extract at doses from 125 to 500 mg/kg p.o. and the reduction at the highest dose (500 mg/kg p.o.) was practically complete. Flavonoid fraction pretreatment also increased mucus production and glycoprotein content. In addition, intraperitoneal administration of indomethacin (10 mg/kg i.p.) to animals treated with the extract (500 mg/kg) partially inhibited gastric protection but the PGE2 determination did not show an increase in prostanoid level. These observations suggest that the gastroprotective effects of the flavonoid fraction from D. viscosa could be partly explained through non-prostaglandin-dependent mechanisms.