Basophilia is not uncommon in the myeloproliferative disorders, particularly chronic granulocytic leukemia. Total blood histamine (contained primarily in the basophils) usually is increased in proportion to the absolute basophilia. However, histamine symptoms are not reported in these situations, in contrast to systemic mast cell disease in which they are the rule. Our patient had chronic granulocytic leukemia with basophilia (basophil count as high as 91,250/cu mm); intense and disabling pruritus, cold urticaria, and epigastric discomfort developed. Total blood histamine exceeded previously reported levels and gastric analysis suggested histamine stimulation. Moderate relief was obtained with antihistaminic agents. No similar case has been described to our knowledge.