Colonization of Helicobacter pylori (HP) beneath the protective film of gastric mucus enables the organism to survive in the hostile environment of the gastric mucosa. N-acetylcysteine (NAC), a sulfhydryl compound with potent mucolytic activity, induces a reduction of gastric barrier mucus thickness of about 75% and reduces mucus viscoelasticity. We therefore tested the hypothesis whether better eradication results could be achieved by addition of NAC to omeprazole/amoxicillin (OME/AMOX). 34 HP positive outpatients with endoscopically documented recurrent duodenal ulcer were included in an ongoing, prospective, randomized trial. Exclusion criteria were: alcoholism, previous gastric surgery, or intake of antibiotics, OME, bismuth salts, corticosteroids or NSAIDs within 4 weeks before study entry. Patients currently smoking > 10 cigarettes/day were classified as smokers. HP infection was confirmed by histology (3 biopsy specimens from gastric antrum and 2 from gastric body; H&E, Giemsa) and at least positive rapid urease test or culture. All 34 patients underwent ulcer therapy with OME (20 mg per day) for 20 days (d 1-20). Group A: in 17 patients (5 females, 12 males, mean age 46 [29-74] years; 8 smokers, 9 nonsmokers) the subsequent eradication therapy, consisting of oral OME (40 mg bid) and AMOX solute (750 mg tid) for 10 days, was combined with NAC solute (2 x 600 mg bid (d 21-30). Group B: 17 patients (2 females, 15 males, mean age 39 [19-70] years; 11 smokers, 6 nonsmokers) underwent eradication therapy without NAC (d 21-30). Control endoscopy was done after a minimal interval of 30 days from the end of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)