Kaposi's sarcoma (KS) is the most frequent AIDS-associated neoplasm, and often disseminates to visceral organs, including the lungs. An ante-mortem diagnosis of pulmonary KS is difficult. Recently, DNA sequences resembling a new human herpes virus (HHV-8), have been identified in various forms of KS. We hypothesized that these sequences are present in samples obtained by bronchoalveolar lavage (BAL) in patients with pulmonary KS. Utilizing a nested polymerase chain reaction (PCR), 7/12 BAL cell samples from HIV-infected patients with endobronchial KS were positive for HHV-8 DNA. In contrast, only 2/39 samples from HIV-infected patients without evidence of KS were positive (p = 0.007). Detection of HHV-8 in BAL cells of patients with pulmonary KS was highly specific (95%), with a sensitivity of 58% and a positive predictive value of 78%. In conclusion, HHV-8 is associated with pulmonary KS, and PCR amplification of HHV-8 in BAL cells provides a non-invasive method with a high positive predictive value.