This 50-year-old male was admitted to the hospital on April 1983 with complaints of severe chest pain attacks 2 weeks previously. Laboratory data: On admission the blood findings were Hb 14.3 Gm/dl of blood, RBC 4.70 million/mm3, WBC 11,600/mm3 and a platelet count of 1.1 million/mm3. ECG showed elevation of ST-T in V1 to V4. Serum LDH and CPK levels were high. He was diagnosed as acute myocardial infarction with thrombocythemia. Three days after admission he abruptly fell into a semicomatose state and left hemiplesia. Head computed tomography showed a large, low-density lesion in the right mid-cerebral artery area, and we also diagnosed cerebral infarction. He was given nimustine (ACNU) 100 mg/week three times as remission induction therapy. For maintenance chemotherapy, at first we administered mitobronitol (DBM) 150 mg/day then changed to intermittent administration of ACNU 100 mg. On September 1991, the patient was admitted to the hospital with progressive anemia and uncontrollable thrombocythemia. Bone marrow chromosome analysis revealed aneuploidy. The patient received interferon alpha 3 million unit/day. The thrombocythemia could be controlled but his general condition deteriorated. On April 1992, he died of interstitial pneumonia.