The genotypes of the ABO blood group system were investigated in Korean living in Kangwon-Do area by PCR-RFLP analysis of the seven polymorphic nucleotide positions 261, 467, 526, 646, 703, 796 and 803 of the cDNA from A, transferase. In 253 unrelated Korean individuals, 15 genotypes were found and the allele frequencies of A(Pro), A(Leu), B, O(T) and O(A) were 0.022, 0.209, 0.209, 0.360 and 0.200, respectively, with no deviation from Hardy-Weinberg expectations (chi(2)=2.145, d.f.=6, 0.90<p<0.95). As for the distribution of allele frequencies, a significant difference was noticed between the Korean and a Japanese (chi(2)=30.87, d.f.=4, p<0.001) and a German (chi(2)=127.76,d.f.=4, p < 0.001) populations.