In a prospective study of HIV patients with suspected cytomegalovirus (CMV) disease (n = 144; 140 men, four women; aged 23-69 years, median 38 years; CD4 cells 0-400, median 20/microliters), 242 blood samples were examined for the presence of CMV-pp65 antigen in peripheral blood polymorphonuclear leucocytes by use of monoclonal antibodies and alkaline phosphatase-anti-alkaline phosphatase staining. All patients were thoroughly examined for existing CMV disease at first visit and during follow-up (at least 2 months or until death: 0-24 months, median 14 months). In 43/486 samples of patients with CMV disease, the antigen-test was positive and in 179/194 samples of patients without CMV disease the test was negative, resulting in a sensitivity of 90% and a specificity of 93% for the presence of CMV disease in HIV-infected patients.