A commercial serologic test using purified antigens of Helicobacter pylori has been evaluated in the diagnosis of this infection. In a series of 250 patients undergoing endoscopy with antral biopsies for cytology, histology and culture, serology was positive in 68 of 71 patients with a positive culture (sensitivity: 96 %) and negative in 67 of 69 patients with a normal mucosa and no microorganisms on biopsy (specificity: 97 %). In the entire series, serology was positive in 33 patients with no infection on biopsies (13 %). In a group of 205 blood donors, we confirmed an increasing prevalence with age, ranging from 13 % in subjects less than 30 years old to 38 % in subjects more than 60 years old.