We assessed both the effectiveness of twoHelicobacter pylori(Hp) eradication triple therapies and the usefulness of serology in the follow-up. Fifty patients with active or scarred duodenal ulcer were randomized to lansoprazole or omeprazole for 1 to 4 weeks, with clarithromycin 250 mg twice a day and tinidazole 500 mg twice a day for the first week. Endoscopies were scheduled before treatment, after 8 weeks, and after 1 year.H. pyloristatus was determined before therapy by rapid urease test and histology and during the follow-up by histology and culture. Serology was determined at baseline and at 6 and 12 months. The regimens were equally effective in inducing ulcer healing (95.8% vs. 87.5%) and eradicating Hp with no recurrences at 12 months. Among 44 patients eradicated, a significant reduction of immunoglobulin G (IgG) titer occurred at 6 (p< 0.0001) and 12 months (p< 0.0001). If a titer reduction of more than 30% was taken as an indicator for Hp eradication, the specificity of enzyme-linked immunosorbent assay was 75% at 6 and 95.4% at 12 months with a 100% sensitivity. Either lansoprazole or omeprazole combined with antibiotics are effective in eradicating Hp. Serology is useful for monitoring Hp eradication provided that an appropriate percent reduction in IgG titer is used after more then 6 months after therapy.