Although anti-human leukocyte antigen antibodies (anti-HLA Abs) are important factors responsible for graft rejection in solid organ transplantation and play a role in post-transfusion complications, their role in allogeneic hematopoietic stem cell transplantation (allo-HSCT) has not been finally defined. Enormous polymorphism of HLA-genes, their immunogenicity and heterogeneity of antibodies, as well as the growing number of allo-HSCTs from partially HLA-mismatched donors, increase the probability that anti-HLA antibodies could be important factors responsible for the treatment outcomes. We have examined the incidence of anti-HLA antibodies in a group of 30 allo-HSCT recipients from HLA-mismatched unrelated donors. Anti-HLA Abs were identified in sera collected before and after allo-HSCT. We have used automated DynaChip assay utilizing microchips bearing purified class I and II HLA antigens for detection of anti-HLA Abs. We have detected anit-HLA antibodies against HLA-A, B, C, DR, DQ and DP, but no donor or recipient-specific anti-HLA Abs were detected in the studied group. The preliminary results indicate that anti-HLA antibodies are present before and after allo-HSCT in HLA-mismatched recipients.