The influence of HLA-B27 antigen on clinical, radiological and laboratory features of rheumatoid arthritis (RA) was studied. The group with B27 antigen comprised: 4 males and 20 females aged 28 to 71 and a group of patients free from B27 antigen consisted of 2 males and 21 females aged 26 to 69. RA patients possessing the B27 antigen did not differ regarding the age of the onset of disease, the distribution of affected joints during the follow-up (3-10 years), the development stages of the disease and the presence of rheumatoid factor when compared with B27 negative RA patients. The arthritis of the radiocarpal joints (p less than 0.01) was significantly more often the first sign of the disease in patients with B27 antigen. In these patients low back pain and morning stiffness in the low back were twice as frequent as they were in patients not possessing this antigen. The clinical pattern of the affected spine was also found more frequently in B27 carriers (p less than 0.05). B27 positive RA patients showed also the clinical pattern of sacroiliitis (SI) (p less than 0.05) and x-ray SI (p less than 0.01) significantly more often than the patients free from this antigen. In addition, symmetric arthritis of the peripheral joints was more often diagnosed in patients free from B27 antigen.