Genetic susceptibility to systemic lupus erythematosus (SLE) is conferred not only by various genes within the major histocompatibility complex (MHC) region, but also by several other non-MHC linked genes. The negatively signalling molecule CTLA-4 is involved in establishing and maintaining of peripheral T cell tolerance, which controls T cell activation and reactivity. Its attenuating action helps to prevent an inappropriate initiation of T cell responses to self antigens and to terminate ongoing T cell responses. We tested if there was an association between CTLA-4 and SLE, a disease with B and T cell hyperreactivity and impaired peripheral T cell tolerance.Using the polymerase chain reaction--restriction fragment length polymorphism method with Bbv I digestion, we assessed an exon 1 transition dimorphism (49 A/G) of the CTLA-4 gene in 102 SLE patients and in 76 healthy controls.The distribution of CTLA-4 exon 1 genotypes in the SLE group was significantly different from that in the controls (chi 2 = 6.178, p < 0.05). 17.6% of the SLE patients were G/G homozygotes compared to 5.3% of the controls; 36.3% were A/G heterozygotes vs 40.8% of controls; and 46.1% were A/A homozygotes vs 53.9% of the controls. The frequency of the G allele was significantly higher in SLE patients (35.8%) than in controls (25.7%; chi 2 = 4.142, p = 0.042).Our results indicate that the non-MHC linked CTLA-4 gene could confer susceptibility in SLE, as it does in various other autoimmune diseases (Hashimoto thyroiditis, Graves' disease, IDDM).