Antinuclear antibodies (ANA) were found in 19.1% of patients suffering from ankylosing spondylitis (n = 320). This figure is significantly higher than the results obtained in a control group. ANA were present in all stages of the disease, including the abortive form of isolated sacroiliitis. ANA were also found in different stages of activity. In addition, ANA-positive cases showed a higher inflammatory activity. In females ANA were more frequently found than in males. There was a positive correlation between ANA and HLA B27 in 87.2%.