Airway inflammation is a major factor in the pathogenesis of asthma. Interleukin 8 (IL8) is a potent proinflammatory cytokine that interacts with its receptors, IL8RA and IL8RB. We investigated the genetic polymorphisms in IL8, IL8RA, and IL8RB for any association with risk of asthma and peripheral blood eosinophil counts in a Korean population. By carrying out direct sequencing in 24 individuals, we identified 20 sequence variants within exons and their flanking regions, including the 1.5 kb promoter regions of IL8, IL8RA, and IL8RB. Among them, seven common single-nucleotide polymorphisms (SNPs) were selected for genotyping in our asthma cohort (n = 1,439). Two common haplotypes in IL8 and three in IL8RA and IL8RB (defined as one block) were identified. Although none of the polymorphisms showed a significant association with risk of asthma, IL8RA-B ht2 showed a significant association with the peripheral blood eosinophil counts (%) among asthma patients, e.g., lower eosinophil levels among individuals with the homozygous IL8RA-B ht2 (3.55 +/- 3.39%) than among other asthmatic patients (5.52 +/- 5.55%; P (corr) = 0.018). Our findings suggest that polymorphisms and haplotypes in IL8RA and IL8RB might be among the genetic factors underlying production of peripheral blood eosinophil.