To determine the effect of verapamil on experimental duodenal ulcer, pathologic assessment and secretory study were performed in the rats with ulcerogenic dose of cysteamine. The cysteamine increased gastric acid secretion and produced double duodenal ulcers at the proximal protion of the duodenum. Intramuscular injection of verapamil, 3 hours later, produced a significant decreased in gastric acid secretion which lasted at least 4 hours (cysteamine vs. cysteamine+ verapamil; 63.5 ± 18.4 muEq vs. 25.5 ± 9.0 muEq during the 1st hour after verapamil administration, 83.1 ± 24.2 muEq vs. 27.8 ± 12.3 muEq during the 2nd hour, 110.9 ± 14.4 muEq vs. 38.5 ± 25.9 muEq during the 3rd hour, 116.4 ± 12.1 muEq vs. 40.7 ± 29.6 muEq during the 4th hour, p < 0.001). However, cysteamine-induced duodenal ulcers were not alleviated by two doses of intramuscular verapamil administration (4 mg/kg x 2). It is presumed that suppression of gastric acid secretion may not be sufficient to reduce cysteamine-induced duodenal ulcer formation or that verapamil itself may have aggresive effects against duodenum. To illucidate the exact role of verapamil in cysteamine-induced duodenal ulcer, further studies would be needed.