The ethanolic extract of the Chinese medicinal herb Zingiberis rhizoma, the rhizome of Zingiber officinale Roscoe (Zingiberaceae), was found to show biphasic effects on secretion of cytokines by human peripheral blood mononuclear cells in vitro. In this study, the augmentative effect of Zingiberis rhizoma extract on cytokine secretion was shown to be time dependent. No significant secretion of cytokine was noted when the reaction time was 1 or 3 h. Secretion of interleukin-lp (IL-IP), interleukin-6 (IL-6), and granulocyte-macrophage colony-stimulating factor (GM-CSF) by the mononuclear cells was markedly increased in the presence of a low concentration of Zingiberis rhizoma extract, varying from 10-30 mg/ml, when the reaction time was 18 or 24 h. A higher concentration of the herbal extract did not show similar or stronger augmentative effect as did low concentration of the herbal extract.