In vitro production of TNF-alpha by alveolar macrophages was investigated in 15 AIDS patients with acute interstitial pneumonia and in 4 patients with asymptomatic HIV infection (anti-HIV+) and was compared to that observed in 6 patients with chronic pulmonary disease and in 5 normal controls (undergoing a fiberoptic bronchoscopy for suspected lung malignancy), all 11 HIV negative. Our results show that unstimulated alveolar macrophages of AIDS and anti-HIV+ patients released much more TNF-alpha than subjects with chronic obstructive pulmonary disease or healthy controls did: this overproduction may play a role in the pathogenesis of lung damage infection and particularly in AIDS patients.