The T113M polymorphism resulting from the missense mutation in exon 5 of the human interleukin 9 (IL9) gene was tested for association with bronchial asthma (BA). The genotype frequency analysis did not reveal a deviation from the Hardy-Weinberg equilibrium. A comparison of the genotype frequency distributions in a control group of healthy individuals and in patients with BA suggested an association between T113M and the clinical phenotype. However, this association was not confirmed by the affected family-based association control (AFBAC) or the transmission/disequilibrium test (TDT).