SUMMARY

Seventy-one of 78 patients presenting to routine rheumatology clinics with seronegative arthritis were found to possess the histocompatibility antigen HL-A 27. Four principal components to their arthritis emerged, namely: spondylitis, sacroiliitis, peripheral polyarthritis, oligoarthritis (involvement of one or two large joints). It is suggested that each of these may be influenced by separate genetic determinants. The various combinations in which these occur warrant a unified nomenclature. A small subgroup of patients with HL-A 27-associated arthritis is described in whom the diseases may be especially benign. THE clinical patterns of arthritis in ankylosing spondylitis, Reiter's syndrome, psoriatic and enteropathic arthropathy show considerable overlap and may be indistinguishable. Sacroiliitis and synovitis of the knee can occur alone, in addition to being cardinal features of each of these conditions. Anterior uveitis, genital inflammation, disease of the aortic valve and conduction abnormalities occur in both ankylosing spondylitis and Reiter's syndrome. The histological appearances of keratoderma blenorrhagica closely resemble those of pustular psoriasis (Weinberger et al., 1962) and, and in som