Through the activation of its receptor, interleukin (IL)-4 stimulates the production of total serum IgE level. The IL4 and IL4 receptor (IL4R) chain loci are on genomic regions linked to asthma phenotypes (5q31 for IL4 and 16p12 for IL4R). A functional SNP in the promoter of IL4 has been associated with total serum IgE level,82–84 asthma,82–83,85–87 and other asthma-related phenotypes.86,88–90 SNPs in exons of IL4R have been associated with asthma,95 total serum IgE level,91,96–100 and other asthma-related phenotypes.101–102 Burchard and colleagues89 tested for association between a polymorphism (C-589T) in the promoter of IL4 and two asthma-related phenotypes (FEV1 and total serum IgE level) among 772 patients with asthma. There was a significant difference in the frequency of the T allele between 682 white asthmatic persons and 90 African-American asthmatic persons (0.183 vs 0.544, respectively; p < 0.001). Among white asthmatic individuals, the T allele was associated with an FEV1 of < 50% predicted (p = 0.01) but not with total serum IgE level. Among African-American asthmatic individuals, there was no association between the T allele and either a reduced FEV1 or the total serum IgE level. Ober et al,95 showed that polymorphisms in IL4R differed across three ethnic groups (Hutterites, African Americans, and whites). Although several SNPs in IL4R were associated with asthma and/or atopy in the Hutterites, there was no significant association between any of the five SNPs examined and either asthma or atopy in 56 African-American families. Basehore et al,103 conducted a population-based case-control study of the association between 11 SNPs in IL4R and asthma and total serum IgE level in three ethnic groups (whites, African Americans, and Hispanics). There were significant differences in the frequencies of the SNPs and haplotypes included in the study across the three ethnic groups. Multiple SNPs were associated with asthma and/or total serum IgE level in whites. Among African Americans with asthma (n = 168) and without asthma (n = 269), only one SNP (3017 G/T) was weakly associated with total serum IgE level (p = 0.04), and no SNP was associated with asthma.