In order to examine the clinical efficacy of cepharanthin (Ceph.) for preventing leukopenia caused by chemotherapy in lung cancer patients, a randomized trial was carried out. Subjects were 45 patients with non-small cell lung cancer (NSCLC) receiving initial treatment with cisplatin (CDDP) +adriamycin (ADM) +mitomycin C (MMC). Ceph. was given at a dose of 1 mg/kg to the administration group (Ceph. group) and changes in the peripheral leukocyte count were examined in both the Ceph. and non-Ceph. groups. The Ceph. group showed a reduction in the number of cases with a count nadir less than 3,000/microliters (p less than 0.05), a shortening of the time that leukocyte counts stayed under 2,000/microliters, corresponding to the time in which granulocyte counts were less than 500/microliters (p less than 0.05), and also a reduction of the time for leukocyte counts to recover from nadir to 2,000 or 3,000/microliters (p less than 0.05) measured from the commencement of chemotherapy. These results suggest that administration of Ceph. has an antileukopenic effect in anticancer treatment, and makes it possible to reduce the period of risk for infection, allowing effective regimens to be administered repeatedly in shorter intervals.