An Immunoperoxidase assay was applied to detect early antigens of Cytomegalovirus (CMV) in 150 urine samples from immunocompromised patients, using the commercial available monoclonal antibody against CMV El3. The detection of early antigen by IP (IPCMV) is compared to the conventional cell culture isolation regarding specificity and sensitivity in order to evaluate is usefulness in the diagnostic of CMV infections. The IPCMV showed a sensitivity of 89.8% and a specificity of 91.3% when compared to the isolation method. The great advantage of the IPCMV is based on the shorter time results are achieved, since 48-72 Hs can be enough to provide evidence of CMV infection, while in the isolation technique cytopatho-genic effect was present around 14 days after sample inoculation.