The polymorphisms and haplotypes identified by restriction fragment length polymorphisms (RFLPs) at the apolipoprotein A1-C3 gene cluster (ApoAl-C3) were studied in 75 Han-nationality-Chinese patients with NIDDM, 30 of which were complicated with hypertriglyceridemia. Fifty unrelated healthy subjects matched for age and body weight were chosen as controls. The results showed that after the RFLPs hydrolyzed by the restriction endonucleases SstI and MspI were hybridized with the human ApoAl gene cDNA fragment(l. 0 kb),S2 and M2 tnutational sites consistent with other reports were found . Significant frequency difference in genotype M1M1 was observed between the simple NIDDM and control group(62% vs 42%). In the NIDDM with hypertriglyceridemia group,both of the S2S2 and M2M2 genotypes had a frequency of 10% and the haplotype S2-M2 had a higher frequency than that in controls. This suggests the association of S2M2 haplotype with NIDDM complicated by hypertriglyceridemia.