Randomized, double blind, fixed-sample. A total of 549 subjects were allocated to the vaccine group in which they were treated with highly purified formalin-inactivated virus subunits derived from the plasma of chronic carriers of hepatitis B. A total of 534 were allocated to the placebo group. Both groups received injections at 0, 1 month, and 6 months unless evidence of infection developed before the series was completed.