HCK, a protein-tyrosine kinase belonging to the Src family, is expressed in certain hemopoietic cells and especially prominent in cells of myeloid lineage, particularly mature granulocytes and monocytes (1). HCK gene is located on chromosome sequence 20q11-q12, a region that is affected by interstitial deletions in some acute myeloid leukemias and myeloproliferative disorders suggesting damage to HCK may contribute to the pathogenesis of these conditions (2).