BACKGROUND: Interleukin-4 plays an important role in pathogenesis of asthma, especially in developing atopy by means of switching B lymphocytes to produce IgE. It has been shown that there is polymorphism in the Interleukin-4 promoter region, transversion of cytosine to thymine at-598 from translation initiation site of IL-4 gene. There has also been quite a few works to reveal the role of the polymorphism of IL-4 gene in patients with asthma. We performed this investigation to determine the role of the polymorphism in the severity of symptoms of patients with asthma. We also examined the frequency and the type of the polymorphism in asthmatics compared with non-asthmatics as well. METHOD: The subjects enrolled in this study were 49 asthmatics and 33 non-asthmatics. All the asthmatics were classified as mild and moderate to severe by the NHLBI/WHO Workshop. DNA from both asthmatics and non-asthmatics was extracted, then performed ARMS(Amplification Refractory Mutation System) as well as RFLP using BsmF1 restriction enzyme in order to confirm the polymorphism of IL-4 gene. RESULTS: There was no significant difference in the occurrence of polymorphism of the IL-4 promoter sequence between asthm and non-asthma groups(P=0.7). Among those with polymorphisms, the number of C/C type was slightly more than C/T type in both asthmatics and non-asthmatics, 26 vs 21 in asthmatics and 18 vs 15 in non-asthmatics, which was, however, insignificant statistically. No significant relationship between the severity of asthma and the polymorphism was found(P=0.7). CONCLUSION: There was no significant difference between the severity of asthma and the IL-4 promoter polymorphism(P=0.709). Interestingly, the frequency of the polymorphism in both asthmatics as well as non-asthmatics was found to be even higher than that occurred in Caucasians. However, no significant difference in the frequency of the polymorphism was found in both groups.