From October 1990 to September 1991, 20 consecutive patients with histologically proven malignant pleural mesothelioma (MPM), secondary to environmental exposure to asbestos or erionite, were treated with cisplatin, mitomycin C and alpha interferon (cisplatin 50 mg/m2 i.v. on day 1 of a 21-day cycle; mitomycin C 10 mg/m2 i.v. day 1 of cycles 1,3 and 5; alpha-2b-interferon 10 x 10(6) units i.m., 4 h prior to cisplatin and 10 x 10(6) units i.v. immediately prior to cisplatin day 1 of each cycle). Eighty-two treatment cycles were administered to 19 evaluable patients. Two patients attained a partial response. Eleven patients had stable disease and 6 had disease progression. Toxicities included interferon-related fever and flu-like symptoms, and vomiting. Actuarial median survival was 15 months. Three patients are alive at 20+, 21+ and 27+ months. We conclude that while the addition of alpha interferon to cisplatin and mitomycin C did not result in an objective response higher than previously reported with the cytotoxic agents alone, the trend towards an improvement in median survival as compared to a well-matched historical group suggests some benefit from the inclusion of interferon.