The purpose of this article is to review the molecular genetics of human platelet antigens, the application of molecular biological techniques to detect mutations underlying polymorphisms and the importance of these techniques for clinical medicine of immune-mediated platelet destruction. Review articles, original papers and preliminary (unpublished) observations from our own laboratory are the main source for this article. The nomenclature and phenotype frequency of the platelet alloantigens in different ethnic groups are described. Recent molecular biological advances are also reviewed. It appears that the human platelet antigen systems are due to single base pair substitutions. These mutations create or are responsible for the loss of a target site for a restriction enzyme in one of the alleles. Thus, DNA typing by polymerase chain reaction and subsequently allele-specific restriction enzyme analysis (PCR-ASRA) can be performed.