Immunofluorenscence methods to detect pp65 antigenemia were implemented for identifying the circulating virus-infected cells in individuals known to have cytomegalovirus infection and disease symptoms.Between December-2002 and July-2003, 110 peripheral blood samples were obtained from 46 immunosuppressed patients. pp65 antigenemia and the presence of circulating cells were determined by indirect immunofluorescence using a commercial kit to detect CMV pp65 antigen in peripheral blood leukocytes. Antigenemia was positive when one or more cells was observed with multilobulated, homogenous fluorescent stain in the nucleus. The presence of infected circulating cells (peripheral blood mononuclear cells) was determined when an extended pattern of fluorescent stain was observed throughout the cytoplasm in cells of 35 to 50 microm.Eight antigenemias from 7 patients (15%) were positive. Of these, 4 (57%) were also positive for circulating infected cells and consisted of 3 kidney transplant recipients and 1 liver transplant recipient. The number of positive cells in antigenemia was greater in kidney-transplant recipients than in the rest of immunosupressed patients (457 vs. 1.96, p < 0.005). No association was seen between the presence of infected circulating cells, morbidity, mortality or the development of GVHD (p < 0.001).No correlation was observed between the presence of infected cells, antigenemia and mortality. To substantiate the lack of correlation amongst these factors, prospective studies with larger sample sizes are necessary. These studies will aid in better defining the clinical application in immunosupressed patients.