This update of the JR blood group system (Castilho L, Reid MR. A review of the JR blood group system. Immunohematology 2013;29:63-8) reports new ABCG2 alleles encoding Jr(a-) and Jr(a+w/-) phenotypes, the predominant alleles encoding the Jr(a-) phenotype, and new functional aspects of the ABCG2 glycoprotein. The JR blood group system (International Society of Blood Transfusion system 32) consists of one antigen: Jra.