Forty-five specimens of lymphocytes from HLA-B27 positive subjects were examined by the micro-lymphocytotoxic test with 48 anti-HLA-B27 sera and the results were evaluated statistically by calculation of the correlation coefficient r. Based on the results of the statistical evaluation two groups of sera were determined which determined two groups of lymphocytes, carriers of different HLA-B27 subtypes. Six sera determined subtype B27P1, detected in four lymphocyte samples, another six sera subtype B27P2 found in three lymphocytes. The results of the statistical evaluation correspond to the serological reactions. The results indicate that HLA antigens can be reliably differentiated by simple methods.