HCMV infection is a major cause of morbidity and mortality following kidney transplantation. Clinical diagnosis is difficult, and rapid and sensitive diagnostic methods are needed since antiviral therapy is available. One hundred-forty-five consecutive kidney-transplanted patients were studied during a period of three months after transplantation. For laboratory diagnosis of HCMV infection, we looked for the presence of pp-65 antigen in polymorphonuclear leukocytes, HCMV-DNA and IgM. Demonstration of HCMV pp-65 antigen by immunofluorescence and HCMV DNA by PCR in leukocytes were efficient methods for early diagnosis of infection.