Hepatocyte growth factor (HGF) has been known as a versatile functional molecule, and as being involved in the colony formation of haemopoietic progenitor cells. Clinically, an elevated HGF level in the blood has been associated with liver diseases such as fulminant hepatic failure and acute hepatitis. We have found a high level of HGF in blood and bone marrow plasma from patients with various types of leukaemia and lymphoma. In particular, 21/31 acute myeloblastic leukaemia (AML) patients showed a significant level of HGF (< 0.40ng/ml) in their blood or bone marrow plasma. The mean value of HGF in the plasma of AML patients was 2.03 ng/ml, which was higher than that in the serum of patients with acute hepatitis. This demonstrates, for the first time, evidence of frequent association of increased levels of HGF in non‐lymphocytic leukaemias, though its significance in the disease remains unknown.