We report the cases of two lung transplant recipients (one heart-lung and one single lung) who eventually developed cytomegalovirus (CMV) pneumonitis after documentation of increasing CMV DNA titers in sequential bronchoalveolar lavage (BAL) specimens by polymerase chain reaction (PCR) amplification. To our knowledge, this is the first report that semiquantitation of PCR-amplified DNA can detect an increase in CMV DNA titer in BAL specimens prior to the onset of clinical symptoms or detection of infection by traditional techniques in lung transplant patients. The results obtained in these two cases suggest that DNA titer measurement on sequential BAL samples may differentiate latency from active viral replication and, thus, provide an opportunity for clinical intervention before the development of overt clinical symptoms.