Abstract: One hundred and sixty-six patients with different forms of rheumatic diseases were tissue typed for 26 antigens of the A and B locus of the HLA system, using a modified KN cytotoxicity test. Among 25 patients with confirmed ankylosing spondylitis, 23 had HLA B27 (92 per cent), compared to 2.5 per cent in the normal controls. This confirms the strong association of HLA B27 with ankylosing spondylitis. Eight patients had doubtful AS, five of whom were positive for B27. In 21 patients with mechanical disorders of the spine no B27 was found. Thirty-six patients with osteoarthrosis of the knee joints did not show any significant relationship with any HLA antigens. Twenty-one patients with systemic lupus erythematosus showed an increase of HLA B13 and B17.