Cytomegalovirus-specific lymphocyte proliferation and immunofluorescent antibody responses were measured serially in five normal adults and eight candidates for renal transplant immunized with Towne strain cytomegalovirus vaccine. All of the normal adults developed cellular and humoral immune responses. Five of the eight immunized renal transplant candidates developed proliferative responses comparable to those of normal adults, although in two instances maximal responses were delayed. Vaccinees developed proliferative responses to antigens prepared from the Towne strain as well as heterologous strains of cytomegalovirus. The appearance of immunofluorescent antibodies was generally delayed for the renal transplant candidates, and two of the individuals who had poor proliferative responses also had low antibody titers.