Detection of cytomegalovirus (CMV) DNA can be facilitated by the polymerase chain reaction (PCR), an in vitro gene amplification technique. Twenty-eight CMV tissue culture isolates were examined by amplification of two separate CMV genes. All were found to contain CMV, although two of the isolates were positive for only one of the two genes. No detectable amplification occurred with human genomic or other viral DNA controls. The amplification products from as few as one CMV plaque-forming unit could be detected after the PCR. CMV DNA was detected in the blood of 14 of 27 patients with AIDS and one of six patients who were infected with human immunodeficiency virus but who did not have AIDS. Normal CMV-seropositive or -seronegative individuals did not have CMV DNA detected in their blood. The CMV PCR was more sensitive than the standard culture assay, can be completed in one to two days, uses only 20 microL of blood, and may be useful for rapidly detecting CMV in clinical specimens.