Recent advances in molecular and cellular biology have made it possible to build upon previous serological and biochemical studies of human platelet alloantigen systems in important and exciting ways. In addition to providing a detailed basic understanding of the polymorphisms that are responsible for eliciting an alloimmune response, the molecular characterization of platelet membrane glycoprotein polymorphisms is expected to have an increasingly large clinical impact. As the molecular basis of the remaining platelet antigen systems becomes known, our ability to design novel diagnostic and therapeutic approaches for the care and management of patients with PTP and NATP should improve.