Laboratory signs and clinical symptoms observed in three cases of coexistent PV+CML were as follows: high WBC in 3/3 cases (11, 22, 39); high HB level in 1/3 (11), high HCT in 1/3 (11), EPO level below normal level in 1/3 (11), basophilia and eosinophilia in 1/3 cases (22) as well as splenomegaly (22). The gene discussed is EPO; the disease is Splenomegaly.