The authors followed the frequency of errors in serologic identification of HLA-A and HLA-B antigens. They analyzed 205 paternity cases evaluated independently by two judicial experts (a revision of expert opinions). The specification of revealed discrepancies is demonstrated in the study and possible causes of their origin are analyzed. In the conclusions the authors recommend useful steps leading to the decrease of error frequency in HLA antigen typing. The HLA system--the major histocompatibility system of a man, has a broad utilization in the field of practical medicine. HLA compatibility should be respected in the choice of the couple donor-recipient for transplant therapy. HLA, as a highly polymorphic system, is successfully applied in forensic medicine. A strong association with some diseases makes it possible to utilize HLA as a supporting diagnostic sign. The commission for nomenclature of WHO at XI. International Histocompatibility Workshop (1991) recognized the following numbers of HLA specificities: 25 A, 55 B, 10 C, 21 DR, 9 PQ, 6 DP. At present HLA laboratories used mostly serological methods. The need to mutually differentiate HLA antigens which are similar due to their molecular structure puts an extraordinary demand on HLA laboratories. On one hand, a great number of HLA phenotypes exist in the population, which ensures the identification of every individual and the distinguishing of self-nonself components. On the other hand there appear the limited possibilities of HLA laboratories with relatively low numbers of diagnostic sera. We inquired how often errors occurred in HLA antigens determination. We chose a set of 205 auditing experts opinions of paternity cases for analyzing the problem.(ABSTRACT TRUNCATED AT 250 WORDS)