AbstractThe frequency of restriction fragment length polymorphisms (RFLPs) of the apolipoprotein B (apo B) gene, detected byXbaI andEcoRI, and their influence on serum lipids and apolipoproteins were studied in healthy Chinese of both sexes in Singapore. A total of 221 subjects (150 males, 71 females) were investigated for theXbaI and 159 subjects for theEcoRI polymorphisms, while serum lipids and apolipoprotein levels were available for 196 subjects. The frequency of theX2allele was found to be significantly lower in the Chinese than that reported in Caucasians from the United Kingdom (0.09 vs. 0.51,P<0.001). The haplotype frequencies were also significantly different between the Chinese and Caucasians with a higher frequency ofXlRlin the former compared to the latter (0.85 vs. 0.34,P<0.0001). The distribution of RFLP genotypes at both of the restriction sites was atHardy‐Weinbergequilibrium in all groups. The influence of the apo B RFLPs on serum lipids and apolipoprotein levels (apo AI, AII, and B) was studied by both residual and multiple regression analyses considering age, sex, body mass index (BMI), and genotypes as independent variables in all possible combinations. No association was observed between the apo B genotypes and serum lipids or apolipoprotein levels except for high density lipoprotein cholesterol (HDLC), apo AI and AII, with theX2being associated with significantly lower levels of HDLC as well as apo AI and AII, the effect being stronger in males. These data raise the possibility that the mechanism of reported association between apo B polymorphism and coronary artery disease may be through effects on HDLC. © 1992 Wiley‐Liss,