Live attenuated Towne strain cytomegalovirus vaccine was evaluated in healthy volunteers and renal transplant recipients. Immunization induced humoral and cell-mediated immune responses in both groups, although responses were of a higher magnitude in healthy volunteers. Immunization of candidates for renal transplantation with Towne vaccine significantly reduced the incidence of moderately severe and severe cytomegalovirus disease in high-risk recipients after transplantation. Reactivation of vaccine-strain virus was not detected. While the use of live attenuated Towne strain vaccine for prevention of primary cytomegalovirus infections in solid-organ transplant recipients and pregnant women deserves further consideration, efforts are also under way to develop a subunit cytomegalovirus vaccine.