67 patients with ankylosing spondylitis (AS) were tissue-typed for HLA-A, -B and -C antigens. HLA-Bw62 was found in 6 of 13 (46%) HLA-B27 negative patients, compared to 9% in HLA-B27 positive AS (p greater than 0.01) and 10% in healthy blood donors (p greater than 0.001). HLA-Bw62, a split of the previous HLA-B15, belongs to the HLA-Bw35 CREG antigens, 11 of 13 (85%) of HLA-B27 negative patients had an HLA-Bw35 CREG antigen. The present results are interpreted as an indication of a direct involvement of the HLA-B locus in the pathogenesis of AS.