A phase II study of MCNU tablet has been performed on 70 patients with hematological disorders including mostly myeloproliferative disorders. MCNU tablet was given p.o. at a dose of 50 mg daily for 2-6 days (total 100-300mg) as one course with average intervals of 3 to 5 months or more for patients responding to this drug. The effective rates were 72% in 18 patients with chronic myelogenous leukemia, 88% in 25 patients with polycythemia vera and 68.5% in 19 patients with essential thrombocythemia. Side effects of MCNU tablet were nausea and vomiting (31%) which had a dose-dependent relationship, mild liver dysfunction (5%) and elevation of BUN and creatinine (2%) which were not serious. The results were almost comparable to those of the phase II study of MCNU given intravenously.