A 38-year-old Japanese man had suffered from trichophyton infection for several years. The white blood cell count was 20,300/mm3, including 54% abnormal lymphocytes with irregularly convoluted nuclei. Adult T-cell leukemia (ATL) was diagnosed based on proliferation of CD4-positive lymphocytes, positive anti-HTLV-I antibody and monoclonal integration of proviral DNA. By 30 mg/day of ubenimex (Bestatin), the abnormal lymphocytes positive for CD4 in the peripheral blood were gradually reduced. Complete remission was maintained for 9 months without any antineoplastic agents. Ubenimex may have suppressed the growth of ATL cells in this patient. Accordingly, ubenimex may prove useful for treating some patients with chronic-type ATL.