Abstract: The present invention is intended to provide a technique relating to a method of specifying an SNP which comprises repeating presumption of an SNP serving as a marker and detailed typing of SNPs around the same, thus gradually narrowing down the focus to the base sequence domain in which the ‘target’ SNP is likely contained and finally specifying the ‘target’ SNP at a high efficiency. As FIG. 1 shows, the method of specifying an SNP comprises: (1) determining a drug to be developed which is the subject of the determination; (2) collecting samples to be analyzed; (3) determining a ‘scanning domain (base sequence domain)’; (4) determining ‘typing’ SNPs; (5) SNP typing by the wet process and analyzing haplotypes based on the typing data; (6) presuming a ‘marker’ SNP (determining the analytical data); and (7) specifying the ‘target’ SNP (target SNP). A cycle consisting of the stage (1) to (7) is repeated as a treatment cycle.