Seventy out of 125 patients with HIV infection had diffuse alveolo-interstitial pneumonia usually caused by an opportunistic infection, notably pneumocystosis. Nineteen patients had only localized lung opacities due either to usual or tuberculous bacterial infections or to Kaposi's sarcoma. In 10 patients with pleural effusion or mediastinal adenopathy, the condition was due to Kaposi's sarcoma (n = 4) or to mycobacteriosis (n = 3). An opportunistic or usual infection was demonstrated in 17 of the 51 patients with normal radiography of the chest. Finally, 37 patients free from infectious or tumoral pathology had isolated lymphocytic alveolitis.