The purpose of this study was to retrospectively review our experience with a consecutive group of 41 renal transplant recipients (R) who received a kidney from a cytomegalovirus (CMV) seropositive donor (D(+)) and had 3 months of prophylaxis with oral ganciclovir. Patients were prospectively monitored clinically and with determinations of CMV antigenemia for at least 6 months. Patients were followed for a mean period of 247+/-16 days. CMV antigenemia developed in 51% of patients (53% D(+)R(-), 47% D(+)R(+)) after the transplant, but in no case was antigenemia seen during the period of oral ganciclovir therapy. Antigenemia developed at a median of 167 days post transplant (range 99-522 days) and peak antigen counts ranged from <1-3940, and tended to be higher in D(+)R(-) recipients. Infection was symptomatic in 67% of the antigenemic patients and symptoms tended to be more marked in the D(+)/R(-) than in the D(+)/R(+) group. All symptomatic patients were treated with intravenous ganciclovir (21 days) followed by 9 weeks of oral ganciclovir and responded with resolution of symptoms and antigenemia. No evidence of tissue-invasive disease was seen. Recurrence of antigenemia was observed exclusively in the D(+)R(-) group, occurred with less severe manifestations of CMV infection, and invariably responded to retreatment with ganciclovir. Our results suggest that oral ganciclovir prophylaxis is effective in preventing CMV infection during the 3-month period of prophylaxis, that a 3-month period of prophylaxis appears to be sufficient for D(+)R(+) recipients, but a longer period of oral ganciclovir prophylaxis may be needed in D(+)R(-) recipients. Clinicians caring for renal transplant recipients should be vigilant to the possibility of late CMV infection, especially in D(+)R(-) recipients.