Allele frequencies at six RFLP sites (Ins/Del, ApaLI, AluI, XbaI, MspI, and EcoRI) of the apolipoprotein B gene (APOB) and the relationship of genotypes with plasma lipid and lipoprotein levels in the Mongolian Buryat were investigated. Common alleles at these sites in 110 Buryat subjects were I, G, A-, X-, M+, and E+; the frequencies of 0.809-0.991 differed strikingly from those of a few Asians and most Europeans. Five unambiguous haplotypes of all sites were revealed at 74%; haplotype IGA-X-M+E+ (000000) was the most frequent (67%), followed by IGA+X-M+E+ (001000) (19%). The frequency constitution differed significantly from the Chinese, Malaysians, and Caucasians but resembled the Indians. No APOB polymorphisms were associated with cholesterol levels (total, HDL and LDL). Significant associations of genotypes were shown with the triglyceride level only at the AluI and XbaI sites. The lipid level of A-A+ females or X-X+ males was higher than that of A-A- females or X-X- males, respectively.