Cepharanthin, a kind of alkaloid, has been reported to show a protective effect for leukopenia induced by radiation therapy. In this study, one of three kinds of drugs, Cepharanthin, S-Adchnon (adrenochrome derivative) and Hythiol (L-cysteine), was randomly administered to 94 patients with cancer of the head and neck, the uterine cervix and the lung, during the course of radiotherapy. When Cepharanthin was given, 81.3% of the patients were protected from leukopenia, compared with 51.6% in S-Adchnon and 32.3% in Hythiol. It is suggested that prophylactic use of Cepharanthin may be useful for cancer radiotherapy.