In 1992, the prevalence of hepatitis B virus (HBV) markers was evaluated in 1004 subjects aged one to 76 years living in urban and rural areas in Tanzania. The overall prevalence rates of hepatitis B surface antigen (HBsAg) and of any HBV marker were 4.4% and 37.0%, respectively. No statistically significant difference by sex was found. The HBsAg prevalence among pregnant women was 4.3% (20/463). The proportion of HBeAg positive among HBsAg positive pregnant women was 10% (2/20). The HBsAg age-specific prevalence was 2.1% in the 1-5 year age-group; peak prevalence (12.1%) occurred in the 6-15 year age-group. Markers of HBV infection were 4.1% by age five years; they increased with advancing age (P < 0.01). Subjects residing in urban areas had statistically significant higher HBV exposure than those residing in rural areas (43.9% vs 27.4%, P < 0.01). Subjects belonging to the largest family size (seven or more members) showed increasing risk (OR 2.9; 95% CI = 1.96-4.28) of HBV exposure. Because maternal HBV transmission early in life appears to be of minor impact and children are mostly infected later in infancy, HBV vaccination at birth is not indicated, while vaccination of all infants at 2-3 months of age with other paediatric vaccinations is the first priority.