The suggested relationship between Borrelia burgdorferi and seronegative spondyloarthropathies has been studied in 125 patients with ankylosing spondylitis (AS). IgG antibodies to Borrelia burgdorferi were present in 11 of 125 patients (8.8%) and in 25 of 125 controls (20%). No patient had clinical Lyme borreliosis. HLA-B27 status was known for 82 patients with AS. There was no difference between B27+ and B27 patients. This study provides no evidence that Borrelia burgdorferi is associated with AS.