Verapamil (3, 10, 20 mg/kg-1) increases the necrotizing effects of oral 25% NaCl or 100% ethanol. Damage by 0.6 N HCl was not equally affected since 1 mg/kg-1 of verapamil decreased the ulcer index whereas the higher doses augmented it. Pharmacologically induced gastric lesions were also differently affected by verapamil, ulcers produced by histamine being greatly enhanced and those of reserpine inhibited. Neither indomethacin nor compound 48/80 ulcers were modified. These results suggest that verapamil modifies the susceptibility of the gastric mucosa to damage.