AbstractHorizontal transmission of hepatitis B virus (HBV) from illicit drug users to their contacts, including young children, can be prevented by active immunization against HBV. Yeast‐recombinant hepatitis B vaccines are now available for this purpose, but their potential efficacy in such high‐risk contacts has not yet been evaluated. Therefore we gave 20 mcg of a recombinant yeast‐derived hepatitis B vaccine to 38 children who were at high risk for HBV infection because they had been institutionalized in a community for drug users in which 8.7% of the occupants are carriers. After third dose of vaccine (at 0, 1, and 6 months), all children had anti‐HBs responses with titers of 10 mlU/ml or more, with 81% showing responses greater than 1,000 mlU/ml. At 12 months, the percentage of anti‐HBs‐positive children was 100%, and the percentage of children with anti‐HBs higher than 1,000 mlU/ml was 56%. None of the children developed HBV infection during follow‐up. Hence the recombinant vaccine was immunogenic, with percentages of seroconversion and anti‐HBs titers comparable with those attained in other categories of high‐risk children with plas