One of the most fascinating areas of research within the field of histocompatibility at present time concerns an observation that a major human histocompatibility system, human leucocyte antigen (HLA), is deeply involved in the development of a great number of diseases. Major histocompatibility complex is the most polymorphic system in the genome of different species. Recognition of HLA alleles could be useful in transplantation and disease studies. Genetic construct of HLA DRB1 was studied in Iranian normal populations and patients with aplastic anaemia and Fanconi's disease. DNA was extracted from the whole blood of 466 normal, 35 aplastic anaemia and 10 Fanconi's individuals. Then DRB1 gene polymorphism was studied by polymerase chain reaction-sequence-specific primer method. The HLA DRB1 gene analysis showed increase of DRB1*07 in aplastic anaemia patients compared to normal population (P = 0.02). According to this study, the frequency of DRB1*07 in normal individuals was 8.3, and in aplastic anaemia patients, 15.7%. Additionally, the frequency of DRB1*04 in normal, aplastic anaemia and Fanconi's individuals was 10, 5.7 and 20%, respectively. Our results of investigation showed correlation between some HLA alleles with the studied diseases. We reported the frequency of various DR types in aplastic and Fanconi's patients. This study could imply the possible role of HLA-DRB1*07 in the incidence of aplastic anaemia. Moreover, the frequency of DRB1*04, DRB1*03 and DRB1*15 alleles showed intermediate correlation with Fanconi's anaemia.