Interferon gamma was first used in 10 patients with mesothelioma in doses of 20 x 10(6) IU administered intrapleurally twice a week for 2 months without success, then in 25 patients (12 in stage I, 11 in stage II or IV) in doses of 40 x 10(6) IU. Out of 20 assessable patients, 4 showed complete response (CR) confirmed at thoracoscopy or thoracotomy; 1 stage I patient and 1 stage II patients showed partial response (PR). Interleukin 2 was administered by continuous intrapleural infusion in increasing dosage. Out of 3 stage I patients, 1 showed CR and 2 showed PR; 4 partial responses were observed in 11 stage II, III or IV patients. The 5/15 CR rate at stage I is exceptional in mesothelioma. In stage II patients the effectiveness and modalities of treatment require further investigations.