Pneumococcal vaccine, 14-valent, was administered to 75 stable adult renal transplant patients on maintenance immunosuppression. 32 had undergone splenectomy prior to transplantation and 43 had not. Functional opsonizing antibody was measured by chemiluminescence methodology for types 12F and 14, contained in the vaccine, and for type 5, a control strain. Serum was examined prior to and at 1 and 6 months after vaccine injection. 33, 71, and 35% of transplant patients had preexisting antibody to types 5, 12F, and 14, respectively, as compared to 58, 87, and 68% of controls. No differences were observed in nonsplenectomized versus splenectomized patients. Following immunization, 59 and 76% of antibody-negative patients converted to positive for pneumococcus type 12F and 14. These included 70 and 70% for nonsplenectomized patients as compared to 50 and 84% for those splenectomized. Vaccination did not result in the production of opsonizing antibody for the related type 5 pneumococcus. Pneumococcal vaccine generates functional antibody and is safe in renal transplant patients.