Recently developed techniques have greatly increased the sensitivity and speed of detection of CMV and of host antibody responses to it. Newer serologic assays such as enzyme immunoassay or latex agglutination assay are accurate and efficient for screening donors and recipients and for determining susceptibility to primary infection. Available IgM antibody assays have occasional utility in recognition of recent infection. The slow process of isolating CMV in cell culture has prompted development of effective rapid techniques that utilize CMV-specific monoclonal antibodies and DNA sequences. Immediate-early viral antigen can be detected in infected cell cultures within hours of specimen inoculation. CMV antigens can also be detected directly in cells within clinical specimens. DNA hybridization has been used for CMV analysis in dot-blot, Southern blot, and in situ hybridization assays; the use of the latter is increasing for the detection of virus in fixed, paraffin-embedded tissue sections. Antigen or nucleic acid detection procedures, when applied directly to relevant clinical specimens, aid in the recognition of tissue invasive disease for which antiviral therapy might be considered. DNA amplification, using the polymerase chain reaction, achieves new levels of sensitivity in viral detection and should be useful for clinical diagnosis and for investigation of CMV pathogenesis and latency.