The aim of this study was to investigate the frequency of the SNPs on MDR1 exon 12, 21 and 26 in Korean population and to analyze haplotype frequency on MDR1 exon 12, 21 and 26 in Korean population. A total of 426 healthy subjects was genotyped for MDR1, using polymerase chain reaction-based diagnostic tests. Haplotype was statistically inferred using an algorithm based on the expectation-maximization (EM). MDR1 C1236T genotyping revealed that the frequency for homozygous wild-type (C/C), heterozygous (C/T) and for homozygous mutant-type (T/T) was 20.19%, 46.48% and 33.33%, respectively. MDR1 G2677T/A genotyping revealed that the frequency for homozygous G/G, heterozygous G/ T, homozygous T/T, heterozygous G/A, heterozygous T/A and for homozygous A/A type was 30.75%, 42.26%, 9.86%, 7.51%, 7.04% and 2.58%, respectively. MDR1 C3435T genotyping revealed that the frequency for homozygous wild-type (C/C), heterozygous (C/T) and for homozygous mutant-type (T/T) was 38.73%, 50.24% and