Antibody responses to pneumococcal polysaccharide vaccine were compared in a control group of 17 normal adults and in a group of 27 adult patients with stable renal function (serum creatinine 0.8--2.1 mg/dl) seven months to nine years following renal transplantation. Using the indirect hemagglutination technique, antibody titers to 13 of the 14 capsular antigens contained in the vaccine were determined for each patient just prior to and again three weeks following immunization. There was no significant difference between the two groups in the proportion of patients responding with a fourfold rise in titer to 12 of the 13 antigens tested. The response rate to antigen type 3 was reduced in the transplant group (p less than 0.05). Mean fold increase in indirect hemagglutination titers was likewise determined for each antigen, and a reduced response in the transplant group was noted only to antigen type 23 (p = 0.037). Immunosuppressed renal allograft recipients appear capable of mounting a nearly normal antibody response to pneumococcal vaccine.