-A prevalence comparison of hypertension among subjects with and those without arsenic exposure through drinking water was conducted in Bangladesh to confirm or refute an earlier observation of a relation in this respect. Wells with and without present arsenic contamination were identified, and we interviewed and examined 1595 subjects who were depending on drinking water from these wells for living, all >/=30 years of age. The interview was based on a questionnaire, and arsenic exposure was estimated from the history of well-water consumption and current arsenic levels. Of the 1595 subjects studied, 1481 had a history of arsenic-contaminated drinking water, whereas 114 had not. Time-weighted mean arsenic levels (in milligrams per liter) and milligram-years per liter of arsenic exposure were estimated for each subject. Exposure categories were assessed as <0.5 mg/L, 0.5 to 1.0 mg/L, and >1.0 mg/L and alternatively as <1.0 mg-y/L, 1.0 to 5.0 mg-y/L, >5.0 but </=10.0 mg-y/L, and >10.0 mg-y/L, respectively. Hypertension was defined as a systolic blood pressure of >/=140 mm Hg in combination with a diastolic blood pressure of >/=90 mm Hg. Corresponding to the exposure categories, and using "unexposed" as the reference, the prevalence ratios for hypertension adjusted for age, sex, and body mass index were 1.2, 2.2, 2.5 and 0.8, 1.5, 2.2, 3.0, in relation to arsenic exposure in milligrams per liter and milligram-years per liter, respectively. The indicated dose-response relationships were significant (P<<0.001) for both series of risk estimates. These results suggest that arsenic exposure may induce hypertension in humans.