Every platelet has natural proteins on its surface. This is well known as human platelet antigen. The HLA (human leucocytes antigens) are important to the platelet membrane and next to ABO system which possess chief barrier to transplantation by the presentation of antigenic peptides T cells. HPLA (the human platelet and leucocytes antigens) are exceedingly polymorphic glycoprotein encoded on the unalike arms of the chromosome. The human leucocytes antigen (HLA) expression is especially high on leucocytes because of their easily availability, and lymphocytes are used to identify the types. Utility of the HLA molecule is in the induction, regulation of immune retorts and in the assortment of T cell repertoire. Also the HLA are effective stimulators, graft versus host disease (GVHD) and graft rejection. Moreover, subsets of HLA B27 and B57 are strongly associated with slow progression of acquired immunodeficiency syndrome (AIDS). This review highlights the human platelet and leucocytes antigens, its importance in antenatal screening, transfusion and in health and diseases.