Infants of mothers positive for HBsAg are at risk for peripartal transmission of hepatitis B infection. Active and passive immunisation administered immediately after birth can prevent neonatal hepatitis B. In a prospective study the prevalence of hepatitis B in pregnant women and the efficiency of selective antepartal screening of women with identifiable risk factors for hepatitis B were analysed. From November 1992 to May 1994, 912 women presenting at the department of obstetrics and gynaecology of the Medizinischen Hochschule Hannover were tested for HBsAg, HBeAg, anti HBs, anti Hbc, and HBV-DNA. Venous blood samples were taken during the third trimester of pregnancy or immediately post partum. 13 (1.4%) patients were found to be HBsAg positive. The prevalence of HBsAg in German females and women from countries with low endemia for hepatitis B was 0.38% versus 5.7% for women from endemic areas. HBeAg was detected in two patients. 10 patients with a positive serological result belonged to groups considered to be of increased risk for hepatitis B infection. Nevertheless, 6 of these women had not undergone antepartal screening. These findings support a need for routine screening of all pregnant women for HBsAg, as it has been recently introduced in Germany.