We have analyzed a dense set of single-nucleotide polymorphisms (SNPs) and microsatellites spanning the T-helper cytokine gene cluster (interleukins 3, 4, 5, 9, and 13, interferon regulatory factor-1, colony-stimulating factor-2, and T-cell transcription factor-7) on 5q31 and the gene encoding the interleukin-4 receptor (IL4R) on 16p12 among Finnish families with asthma. As shown by haplotype pattern mining analysis, the number of disease-associated haplotype patterns differed from that expected for the 129Q allele polymorphism in IL13 for high serum total immunoglobulin (Ig) E levels, but not for asthma. The same SNP also yielded the best haplotype associations. For IL4R, asthma-associated haplotype patterns, most spanning the S411L polymorphism, showed suggestive association. However, these haplotypes consisted of the major alleles for the intracellular part of the receptor and were very common among both patients and controls. The minor alleles 503P and 576R have been reported to be associated with decreased serum IgE levels and changes in the biological activity of the protein, especially when inherited together. In the Finnish population, these two polymorphisms segregated in strong linkage disequilibrium. Our data support previous findings regarding IL4R, indicating that 503P and 576R may act as minor protecting alleles for IgE-mediated disorders.Key Words: asthma, atopy, haplotype pattern mining, polymorphism, association families). The study showed suggestive linkage for asthma (LOD = 2.6) but no evidence for atopy [8]. Although it is not known whether human genes in the 5q31 cytokine cluster are genetic regulators for atopic disorders, experimental models of asthma have shown the importance of both IL4 and IL13 signaling. Administration of either exogenous IL4 or IL13 induced the asthma phenotype in mice [9]. However, neither of these cytokines was able to induce the asthma phenotype in mice deficient in the IL4 receptor (IL4R) [9]. The IL4 receptor is a heterodimer consisting of a common ␥-chain that is shared by several other interleukin receptors (IL2, IL7, IL9, and IL13) and a ligand-specific ␣-chain encoded by IL4R. An IL4R␣-IL13R␣ heterodimer is also able to transduce IL13 signaling [10] and is an important signaling pathway in the asthma model. All this indicates the importance of IL4R␣ in IL4/IL13-mediated signaling.