Serum levels of hepatocyte growth factor (HGF), a potent angiogenic factor, increase during various haematological malignancies. In this study, we examined serum HGF in 59 patients with non-Hodgkin's lymphoma (NHL). Serum HGF levels in NHL patients were increased, as were levels in patients with multiple myeloma, chronic myeloproliferative disorders, and myelodysplastic syndrome. Some 29 patients with T-cell lymphoma, including 20 with adult T-cell leukemia/lymphoma, exhibited a significant increase in serum HGF, as did 23 with B-cell lymphoma. The levels of serum HGF correlated with increased neutrophil counts (r=0.487, p<0.0001), and also paralleled a neutrophil increase in NHL patients who received granulocyte-colony stimulating factor (G-CSF) at the nadir of neutrophil count following chemotherapy. Additionally, in in vitro experiments, HGF secretion from polymorphonuclear neutrophils and its expression in bone marrow myeloid cells were stimulated by G-CSF. Although HGF has been thought to be involved in the pathogenesis of NHL through its angiogenic activities, these results suggest that HGF production by neutrophils and myeloid lineage cells may also contribute to an increase in serum HGF in NHL patients.