The authors relate the results of a clinical study of the Soviet recombination alpha-interferon (reaferon) in 46 patients with chronic myeloleukemia at different stages of the disease. Reaferon is shown to be tolerated well, to have a low percentage of side effects in particular high temperature and allergic reactions, to possess no hepato-, nephro- and cardiotoxicity. It has been proved that in patients with chronic myeloleukemia reaferon produces an independent antiproliferative effect and is capable of controlling the leukemic process without chemotherapeutic drug (in the stable chronic phase of the disease). Doses and administration of reaferon for a long time are suggested in order to prolong the disease course.