The role of hemolysis in the anemia of chronic myelocytic leukemia (CML) remains controversial. The authors reviewed the records of 68 consecutive CML patients to evaluate occurrence and clinical significance of hemolysis. Thirty one (46%) had increased fecal urobilinogen excretion, and this hemolysis group was compared with the remaining 37. There was no difference in age, presence of Philadelphia chromosome, thrombocytopenia, bleeding, occurrence of blast crisis, or chemotherapy in the two groups. There was no correlation between spleen size and hemolysis. Infections and administration of corticosteroids were more frequent in the hemolysis group. Hemolysis was a late complication and had an ominous prognosis, with a temporal association with blast crisis.