Prompted by the reported hypolipidemic activity of garlic, the present study was undertaken to elucidate the mechanism(s) underlying the cholesterol-lowering effects of garlic. Rat hepatocytes in primary culture were used to determine the short-term effects of garlic preparations on [1-14C]acetate and [2-3H]glycerol incorporation into cholesterol, fatty acids and glycerol lipids. When compared with the control group, cells treated with a high concentration of garlic extracts [i.e., petroleum ether- (PEF), methanol- (MEF) and water-extractable (WEF) fractions from fresh garlic] showed decreased rates of [1-14C]acetate incorporation into cholesterol (by 37-64%) and into fatty acids (by 28-64%). Kyolic containing S-allyl cysteine and organosulfur compounds inhibited cholesterogenesis in a concentration dependent manner with a maximum inhibition of 87% at 0.4 mM. At this concentration, Kyolic decreased [1-14C]acetate incorporation into fatty acids by 67%. S-allyl cysteine at 2.0 and 4.0 mM inhibited cholesterogenesis by 20-25%. PEF, MEF and WEF depressed the rates of [2-3H]glycerol incorporation into triacylglycerol, diacylglycerol and phospholipids in the presence of acetate, but not in the presence of oleate. The results suggest that the hypocholesterolemic effect of garlic stems, in part, from decreased hepatic cholesterogenesis, whereas the triacylglycerol-lowering effect appears to be due to inhibition of fatty acid synthesis. Primary hepatocyte cultures as used in the present study have been proven useful as tools for screening the anticholesterogenic properties of garlic principles.