The long-term efficacy of varicella vaccine was studied in 34 children aged 2-18 years who were either on chronic dialysis (n = 17) or were renal transplant recipients (n = 17). Live attenuated virus (OKA line) was inoculated in a single 0.5-ml subcutaneous dose, without modification of the immunosuppressive therapy protocol for renal transplant recipients. The majority of children (85%) developed antibodies within the first 6 months, with IgG titres (enzyme-linked immunosorbent assay) greater than 1:40 (geometric mean 1:640). Of those children who were followed for longer than 2 years, 76% maintained their antibody titres. Reactions to the vaccine were minimal and the immunological protection was effective. Only 3 children developed a mild form of varicella in the post-vaccination period. We consider that seronegative children who are candidates for renal transplantation must be protected against varicella by attenuated varicella vaccination. When vaccination is performed after transplantation, no modification of immunosuppressive therapy is needed.