HL-A types were determined in 90 successive patients with non-granulomatous uveitis. Fifty-one were HL-A27 positive (55.7%) compared to 8.2% of controls. Of 16 patients with ankylosing spondylitis, 13 were HL-A27 positive, as were two patients with a history of Reiter's syndrome. Twenty-eight patients were HL-A27 positive but had no evidence of rheumatic disease. The findings are discussed in relation to the possible pathogenesis of uveitis.