We describe our experience over a three-year period in the detection of antenatal patients with hepatitis B virus (HBV) carriage, and the successful prevention of vertical transmission in the infants of HBsAg-positive women. Nine of the 26 infants born to HBsAg-positive mothers were considered to be at high risk of infection. Eight of these nine remained HBsAg-negative after passive or passive/active immunization. The majority of infants tested had anti-HBs antibody titres above 10 i.u./l from the first month. In comparison with the cost of caring for patients with chronic hepatitis B infection and decompensated cirrhosis, non-selective testing of pregnant women for HBsAg is found to be cost effective.