An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of cytomegalovirus (CMV) in urine using monoclonal antibodies directed against CMV as a capture for viral antigen. The assay was capable of detecting virus at 10(2.3)TCID50/ml as determined by titration of stock virus, strain Ad169. The assay was found to have a sensitivity of 65% and a specificity of 100% when 73 coded stored urine specimens were examined. Assuming that the poor sensitivity was due to loss of antigen following storage, we proceeded to analyse fresh urine specimens. Surprisingly, the assay gave negative results with 46 fresh urines known to contain CMV; however, following storage at +4 degrees C for two weeks, 35 (76%) of these samples gave ELISA results in the positive range. This detection of CMV, after storage at +4 degrees C, could be due to degradation of virus particles leading to release of soluble glycoproteins into the medium or to the presence of an inhibitory substance in fresh urine that is destroyed during storage.