It has been determined that the family of T-cell immunoglobulin domain and mucin domain (TIM) proteins is expressed on T cells. A member of the T<?xm-insertion_mark_start author="Kristin Walton" time="20041115T011745+0100"?>IM<?xm-insertion_mark_end?><?xm-deletion_mark author="Kristin Walton" time="20041115T011747+0100" data="im"?> family, TIM-1, is considered to be a membrane protein associated with the development of Th2-biased immune responses and selectively expressed on Th2 cells. We previously showed that the exon 4 variations of Tim-1 are associated with susceptibility to allergic diseases, as well as autoimmune diseases such as rheumatoid arthritis (RA). In this study, we assessed the association between genotype and allele frequencies of the Tim-1 gene promoter region, in both RA patients and the controls without RA, using polymerase chain reaction-restriction fragment length polymorphism<?xm-deletion_mark author="Kristin Walton" time="20041115T011755+0100" data=" (PCR-RFLP),"?> and single-base extension <?xm-deletion_mark author="Kristin Walton" time="20041110T104858+0100" data="(SBE) "?>methods. We further investigated the relationships <?xm-deletion_mark author="Kristin Walton" time="20041110T114326+0100" data="between"?><?xm-insertion_mark_start author="Kristin Walton" time="20041110T114326+0100"?>among<?xm-insertion_mark_end?> the genotypes of each polymorphism and C-reactive protein <?xm-deletion_mark author="Kristin Walton" time="20041110T104903+0100" data="(CRP) "?>or rheumatoid factor <?xm-deletion_mark author="Kristin Walton" time="20041110T104911+0100" data="(RF) "?>levels in RA patients. The genotype and allele frequencies of the<?xm-deletion_mark author="Kristin Walton" time="20041110T110900+0100" data=" "?><?xm-deletion_mark author="Kristin Walton" time="20041110T110900+0100" data="−1637A>G"?><?xm-insertion_mark_start author="Kristin Walton" time="20041110T110900+0100"?> −1637A>G<?xm-insertion_mark_end?> polymorphism in RA patients are significantly different from those in the non-RA controls (P=0.0004 and P=0.001, respectively). Our results strongly suggest that polymorphism in the Tim-1 promoter region might be associated with susceptibility to RA.