When free radical-scavenging activities of quercetin, alpha-tocopherol, nifedipine and tetracycline were measured by an electron spin resonance technique, all test compounds (10(-5) to 10(-3) M) scavenged both superoxide anions and hydroxyl radicals. The oral administration of quercetin (50 and 100 mg/kg), alpha-tocopherol (8 and 16 mg/kg), nifedipine (20 and 40 mg/kg) or tetracycline (10 and 20 mg/kg) markedly prevented the HCl plus ethanol-induced gastric mucosal injury and the increase in the content of thiobarbituric acid-reactive substances in the injured mucosa in rats. In addition, quercetin (25, 50 and 100 mg/kg), alpha-tocopherol (4, 8 and 16 mg/kg), nifedipine (10, 20 and 40 mg/kg) and tetracycline (5, 10 and 20 mg/kg), given orally, twice daily for 14 consecutive days from the day after acetic acid injection, dose-dependently promoted the ulcer healing and inhibited the increase in the content of thiobarbituric acid-reactive substances in the ulcerated mucosa. These results indicate that quercetin, alpha-tocopherol, nifedipine and tetracycline possess gastric cytoprotective and gastric ulcer healing-promoting actions. In addition, the free radical-scavenging properties of these compounds may be partly related to their anti-ulcer effects.