The c-kit proto-oncogene encodes a transmembrane tyrosine kinase receptor. It is expressed by the primitive CD34 positive haemopoietic stem cells and interacts with the Kit ligand for signal transduction. It was reported to be expressed in over 80% of acute myelogenous leukaemia (AML) patients in North America and Japan. We analyzed 20 AML patients for c-kit expression using either Northern blot analysis or flow cytometry with the YB5.B8 anti-c-kit antibodies. Only 6 out of 20 AML patients expressed the c-kit mRNA or protein product. However, a previously unreported abnormal sized 1.7-1.9 kb transcript was detected in the blast cells of 1 AML patient, 1 acute mixed lineage leukaemia patient and 1 chronic myelogenous leukaemia (CML) patient in myeloblastic transformation. Our data suggested that in most Hong Kong Chinese AML patients, leukaemia transformation may have occurred at a c-kit negative stage. Alternatively, the abnormal sized c-kit transcript that was detected in some Chinese myeloid leukaemia patients may represent an aberrant c-kit receptor that plays an important role in leukaemogenesis.