We discovered a novel single nucleotide polymorphism (SNP) at position 325 (G325A) in exon 5 of the multidrug-resistance 1 (MDR1) gene in a study of 37 healthy Japanese subjects. Details are as follows. SNP, 020614Honda001; GENE NAME, human P-glycoprotein (MDR1); ACCESSION NUMBER, M29427; LENGTH, 25 bases; 5'-ATGAATCTGGAGG/AAAGACATGACCA-3'. This SNP is expected to cause an amino acid substitution (Glu108Lys). In this study, one homozygote and one heterozygote for G325A were identified.