The authors give the results of determining receptors to Klebsiella antigens on the surface of the peripheral blood lymphocytes in ankylosing spondyloarthritis (AS). They examined 21 patients with AS, 20 patients with rheumatoid arthritis (RA) and 20 healthy individuals. Determination of the receptors was done in the reaction of indirect rosette formation. An ultrasonic disintegrate of Klebsiella culture isolated from a patient with AS was used as an antigen. Favourable results were obtained in 10 patients with AS and in none of the cases in the group of patients with RA and in healthy individuals. A higher specificity of the reaction of antigen binding lymphocytes was shown.