OBJECTIVE: A recent study suggested that a single nucleotide polymorphism (SNP) at position nt 9250 (C to T) in exon 7 of the osteopontin (OPN) gene is strongly associated with the susceptibility to systemic lupus erythematosus (SLE). This study examined the possible association between a single nucleotide polymorphism (SNP) at position nt 9250 (C to T) and SLE and measured the serum levels of OPN in Korean patients with SLE. METHODS: A total of 39 patients with SLE and 104 healthy controls were enrolled in this study. SNP located at position 9250 in the OPN gene were genotyped using the restriction fragment length polymorphism (RFLP). The serum levels of OPN in 39 patients with SLE and 20 healthy controls were determined by enzyme-linked immunosorbent assay. RESULTS: The allele frequencies of C and T at this position in patients with SLE were 34.6 and 65.4, whereas those in the controls were 20.7 and 79.3 (p<0.05). The serum levels of OPN in 39 patients with SLE were significantly higher than that in 20 healthy controls (49.13+/-26.71 versus 28.49+/-18.39 ng/ml, p<0.05). The increase in OPN concentration was associated with the SLE disease activity index (SLEDAI) score in all SLE patients (r=0.337, p<0.05). CONCLUSION: The allele frequencies of Eta-1/osteopontin were significantly associated with SLE. Moreover, the increased serum level of OPN is associated with the SLE disease activity. However, further investigation in larger groups in Korea will be needed.