Using a recently introduced multiplex polymerase chain reaction and restriction fragment length polymorphism ABO genotype screening method we have found an anomalous ABO genotype (A2O1variant) not correlating with the serological phenotype (blood group O). The blood group was confirmed by absorption/elution and detection of blood group substances in saliva. Sequencing of exons 6 and 7 in the ABO genes of the propositus indicated an A2 gene (C467T and C1060-) apparently inactivated by the same single nucleotide insertion recently reported in individuals with the ABO subgroup Ael. Investigation of relatives confirmed the inheritance of this new inactive hybrid allele.