The objective of the study was to examine the prevalence and distribution of four major single nucleotide polymorphisms (SNPs) (T59G, T1067G, T202C, and C314T) of the Lewis (FUT3) gene in a biethnic United States population. This population-based cross-sectional study was based on data from the Atherosclerosis Risk in Communities (ARIC) Study, which included 761 males and females aged 45-64 years, who had no known/ detected clinical atherosclerotic disease (577 Caucasians, 184 African Americans). The main outcome measures were prevalence of the Lewis genotype and allele frequencies for four SNPs of the FUT3 gene. The most common genotype was the "wild type" at all four nucleotide positions (WWWW), which was found to be present in 46.9% of ARIC participants. At least one mutant allele was detected in 51.7% of Caucasians, and 56.7% of African Americans (P=0.59). The frequencies of mutant alleles ranged from 6.3% to 18.4% at the four FUT3 gene sites examined. The distribution of the Lewis genotype and allele frequencies differed significantly by ethnicity at sites 59, 202, and 314. The prevalence of the Lewis genotype suggesting a lack of alpha(1,3/1,4) fucosyltransferase activity was 11.6% in Caucasians and 9.9% in African Americans (P=0.67). Four specific SNPs of the Lewis genotype are common in the population at large. However, these four SNPs seem to fail to explain the majority of Lewis-negative phenotype in African Americans, given that Lewis-negative genotype prevalence was about one-third of what was expected. Use of rapid DNA sequencing and simultaneous Lewis phenotype determination could avoid the problems associated with haplotype determination and Lewis genotype grouping. Further studies testing SNPs of the Lewis gene are warranted, in particular among African Americans.