A 53-year-old woman was admitted to our hospital on Nov. 16, 1987, because of general fatigue. On admission, she had hepatosplenomegaly and her peripheral blood profile showed a white blood cell count (WBC) of 309 x 10(3)/microliters with immature neutrophils, a hemoglobin level (Hb) of 7.6 g/dl, platelet count (PLT) of 536 x 10(3)/microliters, neutrophilic alkaline phosphatase (NAP) score of 44. Both Vitamin B12 and LDH levels were high. The bone marrow showed marked myeloid hyperplasia. In a cytogenetic study, Ph1 was found in 3 of 8 metaphases and Ph1 with an additional abnormality of 8 trisomy was noted in 5 of 8 metaphases. She was diagnosed as having chronic myelogenous leukemia (CML) and treated by i.m. injection of interferon (IFN)-alpha at a daily dose of 6 x 10(6) U. Administration of IFN-alpha induced fever for a few days. WBC, PLT count and LDH level gradually decreased, and the NAP score and hepatosplenomegaly improved. She achieved remission in February, 1988. Administration of IFN-alpha was stopped in April, 1988, when the bone marrow showed hypocellularity and normal karyotype. She was treated with 20 mg of prednisolone daily from May until August, because of progressive pancytopenia. She had received no treatment until July, 1989. In May, 1989, the bone marrow again showed myeloid hyperplasia and Ph1 was found in all cells analyzed. Therefore, we resumed IFN-alpha treatment. It is interesting that remission of CML continues for more than one year after discontinuation of IFN-alpha in this case.