This study evaluated the effectiveness of polymerase chain reaction (PCR) combined with a nonradioactive probe for the early detection of cytomegalovirus (CMV) in buffy-coat specimens of immunocompromised patients. Dot-blot hybridization with a digoxigenin-labeled probe was used to detect a 262-bp PCR amplified fragment of the major immediate-early gene of CMV DNA. The results were compared with tissue cultures isolation of CMV. The study included 172 buffy-coat specimens from 72 immunocompromised patients. All 28 buffy-coat specimens positive by culture were also positive by PCR. The remaining 144 specimens were negative by culture; however, 47 of these were positive by PCR. Consequently, PCR was in agreement with culture results in 72% of the samples. Of the 47 PCR-positive-culture-negative specimens, 23 were from patients who had positive buffy-coat cultures at other times during their treatment. Chart review showed that an additional 16 of the PCR-positive-culture-negative samples were from patients with clinical evidence of active CMV disease. The eight remaining specimens were from five patients without signs of active disease. Specimens from 11 healthy volunteers were negative by PCR. In this study PCR was shown to be more sensitive than culture because it allowed earlier detection of viremia and demonstrated CMV in buffy-coat specimens that were negative by culture.