The purpose of this study was to determine whether IL-1 receptor antagonist (IL-1Ra) gene polymorphism is a marker of susceptibility to or severity of systemic lupus erythematosus (SLE) in Chinese patients. The study included 52 Chinese patients with SLE. One hundred and three unrelated, healthy individuals living in central Taiwan served as controls. From genomic DNA, the polymorphism of the gene for IL-1Ra was typed. Allelic frequencies and carriage rates were compared between SLE patients and controls. The relationship between allelic frequencies and clinical manifestations of SLE was evaluated. We found an increased frequency of IL1RN*2 in the SLE patients compared to normal controls (chi(2) = 4.15, P<0.05), with an odds ratio (of allele frequency) of 2.63 (95% confidence interval 1.00-6.96). The carriage rate of IL1RN*2 was also higher in the SLE patients (6.8% in the controls vs. 17.3% in the SLE patients). We observed increased frequencies of malar rash and photosensitivity among patients with IL1RN*2 (77.8%) compared to patients without the allele (48.8%). However, this difference did not reach statistical significance (chi(2) = 2.51, P = 0.11). This study indicated that the frequency of IL1RN*2 is higher in Chinese SLE patients than in Chinese normal controls in Taiwan. However, there was no association between the frequency of IL1RN*2 and clinical manifestations.