We conducted a trial of long-term ganciclovir prophylaxis for prevention of cytomegalovirus (CMV) disease in liver transplant recipients receiving OKT3 therapy for rejection. Intravenous ganciclovir (6 mg/kg once a day, Monday through Friday) was initiated on the same day OKT3 therapy was started and continued for 4 or more weeks. Fifty-one consecutive adult patients (80% CMV seropositive, 20% CMV seronegative) were evaluated. Due to the patient's noncompliance or the primary physician's decision, 6 patients received less than 2 weeks of ganciclovir. Three of these 6 (50%) developed CMV disease (hepatitis 1, CMV syndrome 2). In contrast, of 45 patients receiving 4 or more weeks of prophylactic ganciclovir, only 1 (2.2%) developed CMV disease (hepatitis). There were no cases of CMV disease among 29 patients who received 6 or more weeks of ganciclovir. Reversible neutropenia in 2 patients (4.4%) was the only side effect associated with long-term ganciclovir. Complications from central intravenous catheters did not occur. These results suggest that CMV can be eliminated as a significant pathogen in liver transplant recipients receiving OKT3 for rejection by the long-term administration of prophylactic gnaciclovir, which is safe.