BACKGROUND: The class I major histocompatibility complex (MHC) antigen, HLA-B27 appears to be the major genetic susceptibility factor for ankylosing spondylitis (AS), anterior uveitis, and reactive arthritis, but the mechanism underlying the association remains unknown. HLA-B27 consists of eleven closely related alleles (B*2701-B*2711) which differ in a restricted number of nucleotide substitutions. The aim of this study was to investigate the frequency and the contribution of the HLA-B27 subtypes to AS. METHODS: Forty-six patients (36 AS, 4 anterior uveitis, and 2 psoriatic arthritis, 2 reactive arthritis, 1 erythema nodosum, 1 rheumatic valvular disease) were analysed. The polymerase chain reaction with sequence-specific primers (PCR-SSP) method was used to define B27 allele subtypes. The primers were specifically designed for the discrimination of HLA-B*2701-B*2711. RESULTS: Thirty-two out of forty-six patients were typed. Among them, 27 AS patients were typed. Only two subtypes were identified : 88.9% (24 out of 27) were typed as B*2705 and 11.1% (3 out of 27) were typed as B*2704. Other 5 non-AS patients ( 4 anterior uveitis & 1 psoriatic arthritis) were also typed as B*2705. CONCLUSIONS: No difference in the distribution of HLA-B27 subtypes between patients and healthy controls could be found (Fisher's exact test : P= 0.867, P>0.05). Any specific B27 subtypes don't appear to contribute to AS susceptibility.