Forty men with ankylosing spondylitis have been reviewed clinically, radiologically, haematologically, and biochemically, and the results of the last two compared with a male group of rheumatoid patients and a control group. In the patients with ankylosing spondylitis the haemoglobin levels were much higher and the E.S.R. significantly lower than in the rheumatoid group, and the E.S.R. in the patients with ankylosing spondylitis was unrelated to disease activity as evidenced by pain. The alkaline phosphatase level was raised in 19 cases and in most was derived from bone. Though 10 patients had abnormal globulin levels, the albumin levels were normal, as was renal function in all cases.