Ren-shen-yang-rong-tang (Japanese name: Ninjin-yoei-to, NYT) is a traditional Chinese herbal medicine. Leukocytosis and elevated levels of colony-stimulating factor (CSF) in peripheral blood were found previously after the administration of this compound to mice. In this study, human peripheral blood mononuclear cells (PBMC) were cultured in the presence of NYT in vitro, and the levels of granulocyte-macrophage CSF (GM-CSF) and granulocyte CSF (G-CSF) in the supernatant of cultured PBMC were measured using a sensitive enzyme-linked immunosorbent assays. NYT significantly (P less than 0.01) augmented GM-CSF production but not G-CSF production by PBMC in vitro.