It is known that preconditioning stress may attenuate stress-induced gastric injury and that this effect is mediated by prostaglandins. In the present study we investigated the contribution of glucocorticoids to the gastroprotective effect of preconditioning stress. The effects of mild stress on gastric erosion caused by severe stress were compared in rats with normal and deficient corticosterone response to preconditioning mild stress. Mild stress decreased the gastric ulceration caused by severe stress, and this effect was prevented by glucocorticoid deficiency during mild stress. The results suggest that glucocorticoids released during preconditioning mild stress contribute to the gastroprotective effect of this stress.