Polymerase chain reaction (PCR) amplification of CMV DNA recovered from bronchial alveolar lavage (BAL) and peripheral blood samples was compared with tissue culture, cytology, and/or histology for the earlier detection of CMV pneumonitis in 12 recipients of single-lung or heart/lung transplants. In patients with confirmed CMV pneumonitis, cytological evidence of CMV disease in BAL samples was detected 38 +/- 14 days posttransplantation, while tissue culture and PCR-positive results were noted as early as 30 +/- 4.0 days and 18 +/- 4.6 days, respectively. While PCR was positive earlier than culture in a number of cases, culture-positive results were subsequently obtained in each case, consistent with earlier detection of viral replication by PCR as opposed to detection of latent virus. CMV was detected by PCR in 6 of 24 blood samples from patients with confirmed or suspected CMV pneumonitis, while results of all 24 blood samples were negative when assayed by tissue culture. PCR-based testing was more sensitive than traditional tests, allowing detection of viral replication earlier than tissue culture in the posttransplant period. PCR could provide a powerful means of monitoring the immunocompromised patients in whom preemptive therapeutic intervention for CMV disease is desirable.