A previous article reported a possible relationship between a history of tuberculosis and Helicobacter pylori infection. Epidemiologic similarities exist between the two infections: Mycobacterium tuberculosis and H. pylori are transmitted from person to person and the risk of acquiring them is elevated in underprivileged environment. This study was conducted to investigate the relationship between the two infections. Serum concentrations of anti-H. pylori IgG antibody were measured in 40 tuberculosis inpatients on antituberculosis chemotherapy for no more than 3 months (group I; 52.4 +/- 21.4 years of age), 43 tuberculosis inpatients on it for more than 3 months (group II; 57.3 +/- 16.3 years), and 60 nontuberculosis outpatients (control subjects; 55.9 +/- 16.7 years). H. pylori seropositivities were similar among control subjects (73.3%), group I (65%), and group II (69.8%). The difference in the antibody concentrations was significant between control subjects and group I (353.7 +/- 321.2 vs. 176.5 +/- 197.9 U/ml) but was not significant between control subjects and group II (353.7 +/- 321.2 vs. 229.9 +/- 249.5 U/ml). The seroprevalences may not be different between patients with pulmonary tuberculosis and those without, and antituberculosis therapy may not decrease the antibody concentrations.