In 21 patients with the clinical suspicion of oligosymptomatic R.S.), 21 patients with the clinical suspicion of oligosymptomatic R.S. and 16 patients with recurrent non-gonococcal urethritis 23 HLA-antigens were assessed using a lymphocyte toxicity test. 413 blood donors served as a controll group. 85,7% of the patients with R.S. had phenotyp HLA-B 27 compared with 7,4% of the controll persons. The group with the suspicion of R.S. exhibited with 57,1% a marked increased incidense of HLA-B 27 as well. Compared to this, the HLA-B 27 frequency in the patients with recurrent non-gonococcal urethritis was with 6,3% in especially of its oligosymptomatic courses. Because of the close association between HLA-B 27 and R.S. determination of histocompatibility antigens proved to be a valuable tool in the diagnosis of Reiter's disease, especially of its oligosymptomatic courses.