The spondarthropathy (Sp)-associated HLA-B27 antigen includes at least seven subtypes, B*2701-07, of which 01, 02, 05 and 07 occur in Caucasians. This study examined the B27 subtype distribution in British patients with Sp. The 133 HLA-B27+ subjects comprised 94 European Caucasian Sp (58 ankylosing spondylitis (AS), 22 reactive arthritis (ReA; 11 sexually acquired (SARA), 11 enteric (EReA)), eight undifferentiated Sp (USp), and six pauciarticular juvenile-onset chronic arthritis (pJCA)) patients, and 34 healthy Caucasian controls, together with four Asian Indian and one Chinese. 35S-labelled B27 was immunoprecipitated with anti-B27 MoAbs, and subtyped according to isoelectric point (pI) following isoelectric focussing. The use of B27 MoAb permitted subtype assignment without full class I HLA typing. The vast majority (95%) were B*2705 (Caucasian controls 31/34; AS 55/58; ReA 21/22; USp 8/8, and pJCA 6/6; Indian control 1/1 and AS 2/3; Chinese pJCA 1/1), and the remainder B*2702. No B*2701 or 07 subjects were identified. AS occurs in both B*2702 and 05 subjects, and we extend this observation to small numbers of ReA and of Indian AS subjects. This implicates molecular features shared between B27 subtypes, rather than subtype-determining regions of the antigen, in Sp pathogenesis.