SummaryOf 5,327 pregnant women who were screened between July 1981 and July 1983, 5.2% were found to be hepatitis Bs antigen (HBsAg) carriers. This high percentage of carriers accentuates the importance of vertical transmission of hepatitis B virus in our area. In view of this we sought to verify the effectiveness of hyperimmune immunoglobulins in the prevention of infection. We studied 201 babies born to HBsAg‐positive mothers. These babies had regular checkups until 12 months of age. One hundred forty‐nine received prophylactic hyperimmune globulin (two to seven doses according to risk ranking), while 52 did not. A higher percentage of infection was found in the babies who had no prophylaxis (25%) than in the babies who had prophylaxis (7.4%). Furthermore, hepatitis appeared earlier (from the 2nd to the 6th month) in the babies who had no prophylaxis than in the babies who had prophylaxis (from the 9th to the 12th month). No infection was observed during prophylaxis or up to 6 months.