Cytomegalovirus (CMV) disease is one of the most relevant infectious complications in solid organ transplant, and we must perform an appropriate prophylactic intervention. The goal of this study was to evaluate the effectiveness of prophylactic treatment with valganciclovir in renal transplant recipients in the first three months post transplantation by shell vial urine culture assay, and by measuring antigenemia (pp65) and CMV viral load, the latter by PCR. The population of the study included 100 renal transplant recipients. We analyzed the results of 36 patients recruited between November 2003 and July 2004 who were receiving a prophylactic oral treatment with valganciclovir, and who had finished the follow-up period of 90 days. The three tests mentioned above were performed on days 7, 15, 30, 45, 60, 75 and 90. No positive antigenemia was detected, the virus was cultured in a urine specimen and, in one patient, three measurements of viral load in serum were positive. Preliminary results of the study suggest that universal chemoprophylaxis with valganciclovir is effective for the prevention of CMV infection in renal transplant recipients and that, although all three tests used were useful, the measurement of CMV viral load seems to be the most appropriate method for monitoring these patients.