HCK, a protein-tyrosine kinase, belongs to SRC family members (1). Ziegler et al. found that expression of HCK may be limited to certain hemopoietic cells and is especially prominent in cells of myeloid lineage, particularly mature granulocytes and monocytes (2). Therefore, Quintrell et al. designated the gene HCK (pronounced 'hick') for hemopoietic cell kinase. They described the nucleotide sequence of a cDNA clone and the distribution of RNA transcribed from HCK among various hemopoietic cells. They assigned the HCK gene to 20q11-q12. Since this region is affected by interstitial deletions in some acute myeloid leukemias and myeloproliferative disorders, they suggested that damage to HCK may contribute to the pathogenesis of these conditi