We have evaluated the microbiologic output and clinical significance of the detection of cytomegalovirus in 111 bronchoalveolar lavage specimens from immunosuppressed patients with pneumonitis. The samples were simultaneously processed by conventional tube culture and the rapid shell-vial centrifugation culture assay. Cytomegalovirus was recovered from 30 specimens (27%). The rapid shell-vial procedure was more sensitive than the tube culture, but in two cases cytomegalovirus was isolated only in tube cultures. Cytomegalovirus was considered clinically significant in only 3 from 13 HIV positive patients. All culture positive, HIV negative patients received treatment with ganciclovir. However, ganciclovir was never used on culture negative, HIV negative patients and cytomegalovirus related morbi-mortality was not found in these patients. A prospective study is needed to conclude if a cytomegalovirus negative culture also has a treatment exclusion value in HIV positive patients.