Cytokines appear to be the major regulators of adipose tissue metabolism. Interleukin- 1 receptor antagonist (IL-1ra) serum levels are increased in human obesity, and are under strong genetic control. The hypothesis was tested that the IL-1ra gene might be a candidate for obesity. Furthermore, the relationship was investigated between Sasang constitution and IL-1ra polymorphism. The frequency of a penta-allelic 86-bp tandem repeat (VNTR) in the intron 2 of IL-1ra gene in 67 lean (BMI<25 kg/m2), 133 overweight (BMI 25-29.9 kg/m2) and 61 obese (BMI>or=30 kg/m2) otherwise healthy Korean subjects was investigated. Total fat mass and percentage body fat were determined by dual-energy X-ray absorptiometry. Subjects were discriminated into four types by QSCC II program as well as clinical data (weight, height, blood pressure, etc.); Teaeumin, Taeyangin, Soyangin, and Soeumin. Genomic DNA was extracted and used for polymerase chain reaction-based genotyping of IL-1ra. The genotypic, or allelic distribution did not differ markedly between the three groups. The relative risk of being obese in comparison with lean was twofold increased in allele 2 carriers, although it was not statistically significant. Carriers of the allele 2 did not show a significant difference in physical and clinical characteristics. However, the relative risk of being obese in comparison with lean was increased in Taeumin subjects (p=.050), and so was in IL-1ra A2- carriers (p=.047). No relationship was found between the IL-1ra polymorphism and BMI in Korean women, but the authors first attempted to find an association among IL-1ra polymorphism, obesity, and Sasang constitution.