Current management of renal transplant recipients who are CMV seronegative (R-) and receive an organ from a seropositive donor (D+) is controversial. These patients are at high risk for CMV disease and are usually treated with ganciclovir prophylaxis at variable dose and duration. An alternative to this approach is to administer ganciclovir only to those patients who are identified by virological markers to be at the highest risk to develop the disease (preemptive therapy). This prospective trial was conducted to asses the value of preemptive therapy to prevent CMV disease in R-/D+ kidney transplant recipients on triple drug immunosuppression without antilymphocyte induction. Sixteen adults receiving their first kidney transplant were enrolled and followed with pp65 antigenemia assay performed biweekly for the first 16 postransplant weeks, and then monthly to complete 12 months. Ganciclovir (5 mg/kg/day i.v., for 15 days) was administered as preemptive therapy upon detection of one or more antigen-positive cells per 150 x 10(3) peripheral blood leucocytes examined. For those receiving preemptive therapy, pp65 antigenemia was also repeated after completion of the regimen. CMV antigenemia was detected in 7/16 patients. At mean follow-up of 9 months (4-12 m) none of the 16 patients developed CMV disease. CMV serology (IgM) became positive in all patients after the first antigenemia result. The last follow-up mean serum creatinine (SCr) level was similar in both groups (1.35 mg/dL). In CMV R-/D+, the use of preemptive therapy guided by pp65 antigenemia is effective in preventing CMV disease. By using this strategy, 9 of 16 patients were spared ganciclovir prophylaxis with no effect on rejection or CMV disease. The clinical benefit and cost/effectiveness of this strategy should be evaluated against universal prophylaxis in these high-risk patients.