To evaluate the immunogenicity of hepatitis B vaccine in renal transplant recipients, we administered three 40-μg doses of vaccine to 17 patients who had previously undergone transplantation and were on immunosuppressive therapy. Life-table analysis revealed a cumulative antibody response rate of only 17.6% at 12 months, and the three responders had low titers of antibody to hepatitis B surface antigen. There were no serious adverse effects and no episodes of graft rejection in responders or nonresponders. In addition, the ratio of helper/inducer (T4) to suppressor/cytotoxic (T8) T cells in vaccinees bore no relationship to the immunogenicity of the vaccine. These data indicate that hepatitis B vaccine is weakly immunogenic in renal transplant recipients and illustrate the need for vaccination prior to transplantation for maximal protection against hepatitis B virus infection.