This study was intended to observe the effects of insulin on synthesis and secretion of apolipoproteins by hepatic cells. The HepG2 cells were cultured in RPMI 1640 media with bovine insulin (1 microgram/ml media and 10 micrograms/ml media) for 72 hours, and the apolipoproteins contents in cultured media were measured by radioimmunodiffusion assay (RID) kits developed by authors' research laboratory. 40 fold lyophilizely condensed culture media were used for the assays. The results showed that the relative amounts of apo A I, A II, B100, C III and E secreted by HepG2 cells detected by this method were 824 +/- 27, 813 +/- 24, 4875 +/- 82, 597 +/- 74 and 97 +/- 4 ng/mg cell protein, respectively. When 1.0 microgram/ml medium of bovine insulin was added into the culture media, apo A I and apo E secretion remained unchanged. When compared with the control, while apo A II tended to decrease, apo C III tended to increase, and apo B100 secretion decreased by 21.2%; when 10.0 micrograms/ml medium of insulin was added, apo A I, A II and B100 secretion decreased by 6.9% (P < 0.05), 44.3% (P < 0.01) and 29.3% (P < 0.01) respectively, while apo C III secretion increased by 51.8% (P < 0.01). These results support certain parts of the hypothesis of pathogenesis of Chinese endogenous hypertriglyceridemia proposed by Bing-Wen Liu.