Cytotoxic T-lymphocyte antigen 4 (CTLA4) polymorphisms located in the promotor region at positions -318 (C/T) and in exon 1 (49 A/ G) were investigated in 138 Spanish patients (37 men and 101 women) with rheumatoid arthritis and in 305 ethnically-matched healthy controls. When the allelic and genotypic frequencies corresponding to the CTLA4 -318 position were compared, no significant differences between patients and controls were found. However, when the CTLA4 49 A/G polymorphism was analysed, a significant increase of A/G heterozygous individuals among female patients (48.5% vs. 33.8% in controls; P=0.008; OR=2.0) was observed. This increase was absent among males (37.8%, P=NS). Analysis of the CTLA4 49 polymorphism with respect to HLA-DRB1 typing demonstrated a significant increase of A/G heterozygosity in the HLA-DR3-positive patient group compared with HLA-DR3-negative patient group (14/19, 74% vs. 49/119, 41%; P=0.009, OR=4.0). The increase of A/G genotype among HLA-DR3-positive patients was found in both males (4/6, 67%) and females' (10/13, 77%), although statistical differences were only reached in the female group. These results provide new insight into this complex association, confirm previous data from other studies, and suggest that the CTLA4 gene could be involved in the pathogenesis of rheumatoid arthritis.