Because of the risk of serious pneumococcal infections in patients receiving a renal transplant, a study was undertaken to determine if pneumococcal vaccine could be administered before or after transplantation. Vaccine was given to recipients of transplants and to patients who were undergoing dialysis. Both groups responded to the vaccine, and although the mean antibody levels were lower than those reported for normal populations, the levels were in the range thought to be protective for most pneumococcal types. Antibody levels, both before and after vaccination, were substantially lower in patients with recent transplants than in patients who were undergoing hemodialysis. Patients who are awaiting renal transplantation can be immunized while they are undergoing hemodialysis. Further study is needed to determine how long antibody levels will persist after vaccination in both patients undergoing hemodialysis and those receiving a transplant.