The frequencies of HLA-A, -B, and -DRB1 alleles and A-B-DRB1 haplotypes were studied in 510 healthy unrelated Koreans, using serological (for A, B) and polymerase chain reaction (PCR)-single strand conformation polymorphism (for DRB1) methods. A total of 35 DRB1 alleles were detected and the most frequent alleles were DRB1*1302 (10.9%), *0901 (9.5%), *1501 (8.2%), *0803 (7.3%), *0405 (7.3%), *0101 (6.4%), *0406 (6.0%), and *0701 (6.0%). HLA-DR4 and DR14 groups were most polymorphic, each group composed of eight DRB1 alleles. Two-locus associations between HLA-DRB1 and -B loci were analyzed. There were 16 A-B-DRB1 haplotypes occurring at frequencies of > or =1%, and the five most common haplotypes were A33-B44-DRB1*1302 (5.4%), A33-B58-DRB1*1302 (3.7%), A33-B44-DRB1*0701 (2.9%), A24-B7-DRB1*0101 (2.2%), and A24-B52-DRB1*1502 (2.0%). Comparison of the distribution of A-B-DRB1 haplotypes among East Asian populations revealed that Koreans are closest to Japanese, out show a higher degree of polymorphism compared with Japanese.