Alpha interferons have shown significant antitumor activity against B-cell malignancies (especially hairy cell leukemia), and chronic myelogenous leukemia. They are also useful against malignant carcinoid tumors, renal cell carcinoma, and Kaposi's sarcoma. Alpha interferons are less effective against lung, liver, ovary, breast, and colon carcinoma. Side effects vary in severity according to type of interferon, route of administration, schedule, and dose. In general, tolerance and compliance are excellent with doses of one to nine million units per day.