ABO polymorphism at the gene level has been investigated by molecular methods, predominantly sequencing and restriction fragment length polymorphism (RFLP). We describe the application of the polymerase chain reaction-sequence specific oligonucleotide (PCRSSO) method, which is considered to be more versatile for large sample numbers, compared with conventional ABO genotyping by PCR-RFLP. PCR-SSO, while maintaining accurate and reliable results, reduces costs and labor. A population of 155 random individuals was investigated for the three O alleles, O1, O1*, and O2. The allelic frequencies were 35 percent, 26 percent, and 5 percent, respectively. PCR-SSO results correlated completely with both serologic and PCRRFLP results.