The pharmacological effects of Dai-saiko-to, a Japanese and Chinese traditional medicinal mixture (Kampohozai), on lipid biosynthesis were investigated in cultured human hepatocyte HepG2 cells. The addition of Dai-saiko-to (0.5 mg/ml), which had no significant effect on cell proliferation, caused a marked decrease in the intracellular triglyceride content with no significant changes in the other lipid fraction. At the same time, the incorporation of 14C-acetate or 3H-glycerol into the triglyceride or diglyceride fractions also decreased significantly. These results suggest that Dai-saiko-to decreases hepatic triglyceride biosynthesis, which might contribute to a reduction in plasma VLDL levels.