From June 1978 until August 1981 4400 pregnant women were consecutively investigated in Vienna for the presence of hepatitis B. 23 women (0.52%) were HBs-antigen positive; 15 of these were foreigners (from Yugoslavia, Turkey, Philippines, Rumania),22 pregnant women were healthy HBs-antigen carriers. One woman had an unspecific reactive hepatitis. Three pregnant women were HBe-antigen positive, 18 anti-HBe positive. Hepatitis B infection was detected in three children of HBs-positive mothers. The highest risk of infection existed in children of HBe-antigen positive mothers. There was no connection between the infection of the children and HBs-antigen in cord blood, delivery and breast-feeding habits. Hepatitis infection took a different course in the three children: one child was an HBs-antigen carrier with a healthy liver, whilst in two children seroconversion took place and anti-HBs was formed without clinical-biochemical signs of hepatitis. Measures for the prevention of vertical hepatitis B transmission are discussed.