Pantoprazole is a newly developed benzimidazole derivative with strong inhibitory actions on gastric acid secretion by blocking H(+)-K(+)-ATPase. This randomized double-blind multicenter trial investigated the efficacy of 20 mg, 40 mg and 80 mg pantoprazole o.m. on ulcer healing and symptomatic relief in 219 out-patients with endoscopically assessed acute duodenal ulcer. After 2 weeks complete ulcer healing was achieved in 58%, 89% and 82% of the patients with 20 mg, 40 mg and 80 mg pantoprazole o.m., respectively. After 4 weeks, corresponding figures were 93%, 99% and 100%; the difference of the healing rates between the 20 mg and 40 mg groups at 2 weeks was statistically significant (p < 0.0001). A rapid pain relief was achieved in all treatment groups: 72% of the 20 mg group, 89% of the 40 mg group, and 84% of the 80 mg group were pain-free after 2 weeks. The difference between 20 mg and 40 mg was statistically significant (p < 0.05). Pantoprazole was well tolerated. Adverse events occurred in 13 patients; headache, skin alterations, and diarrhea were reported most frequently. Severity and frequency of adverse events did not reveal any dose-dependence. In conclusion, pantoprazole provides fast healing of acute duodenal ulcer as well as rapid improvement of ulcer symptoms. For further clinical trials in peptic ulcer disease a daily dose of pantoprazole 40 mg o.m. is recommended.