The CMV pp65 antigenemia test is an immunofluorescence-based assay which utilizes an indirect immunofluorescence technique for identifying the pp65 protein of cytomegalovirus in peripheral blood leukocytes. The CMV pp65 assay is widely used for monitoring CMV infection and its response to antiviral treatment in people who are under immunosuppressive therapy and have had renal transplantation surgery, as the antigenemia results are obtained about 5 days before the onset of symptomatic CMV disease. The advantage of this assay is the rapidity in providing results in a few hours and that the pp65 antigen determination represents a useful criterion for the physician to initiate antiviral therapy. The major disadvantage of the pp65 assay is that only a limited number of samples can be processed per test batch.