The genotypes of genomic DNAs of 20 normal subjects with ABO blood group and 12 subjects with cisAB blood group were analysed using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) and a combination of PCR-RFLP and direct sequencing method, respectively. To identify the codon 87, 249 bp DNA fragment was amplified by PCR and digested with Bst EII and Kpn I. To identify the codon 176, 506 bp DNA fragment was amplified by PCR and digested with Bss HII and Ban I. To identify the codon 235, 266 and 268, 506 bp DNA fragment was amplified by PCR and determined by direct sequencing. Analyses of the digested DNA fragments of codon 87 and 176 in 20 normal subjects with ABO blood group revealed the ratio of homotype (AA, 20%; BB, 20%) and heterotype (AO, 80%; BO, 80%) in subjects with phenotype A or B. Same results were obtained in subjects with phenotype AB or O. The analyses of nucleotide sequence at codons 87, 176, 235, 266 and 268 in 12 subjects with cisAB blood group (6 cisA2B3, 3 cisA2 B and 3 cisA1B3) revealed chimera structure of A allele and B allele on the same gene. These results indicate the usefulness of PCR-RFLP method for determining the genotype of A and B bloods group, and a combination of PCR-RFLP and direct sequencing for determining the genotype of cisAB blood group.