Objectives: To date, some studies have suggested that short-term therapy may be a promising therapeutic concept for the eradication of Helicobacter pylori. The primary objective of the present study was to elucidate the role of the duration of treatment in the cure of H. pylori infection. Methods: Forty consecutive patients with H. pylori-positive peptic ulcer disease were randomly allocated to four study groups. The groups were treated with a 14-day course of 20 mg omeprazole b.i.d. orally combined with 2 g amoxicillin t.i.d. intravenously for 1 day (n = 10; six women, age range 40-84 yr), for 3 days (n = 10; three women, age range 29-74 yr), for 5 days (n = 10; five women, age range 21-82 yr), and for 7 days (n = 10; five women, age range 42-82 yr), respectively. Initially, a standardized clinical evaluation of symptoms and an upper GI tract endoscopy were performed for assessment of H. pylori infection of the gastric mucosa (biopsy urease test, specific culture, and histology). At least 4 wk after cessation of omeprazole medication, H. pylori eradication was evaluated either as described or with the help of the C-13-urea breath test. Results: H. pylori eradication, defined as negative bacterial findings in urease test, culture, and histology or C-13-urea breath test at least 4 wk after discontinuation of omeprazole therapy, was achieved in one of 10 patients (10%) in the one-day group, none of 10 patients (0%) in the 3- and 5-day groups and six of 10 patients (60%) in the 7-day group. Conclusions: We conclude that short-term therapies with the proton pump inhibitor omeprazole and the antibiotic amoxicillin must be considered completely ineffective if performed as a short-term therapy for up to 5 days. A therapy duration of 7 days seems to mark a turning point in antibiotic effectiveness, with a rapid increase in eradication rates.