Individualization of drug therapy through genetic testing would maximize the effectiveness of medication and minimize its risks. Recent progress in genetic testing technologies has been remarkable, and they have been applied for the analysis of genetic polymorphisms that regulate drug responses. Clinical application of genetic information to individual health care requires simple and rapid identification of nucleotide changes in clinical settings. We previously reported a novel DNA diagnostic method for detecting single nucleotide polymorphisms (SNPs) using competitive allele-specific short oligonucleotide hybridization (CASSOH) with an immunochromatographic strip. We have developed the method further in order to incorporate an enzyme-linked immunosorbent assay (ELISA) into the final detection step; this enables multiple SNP detection. Special ELISA chips have been fabricated so that disposal of buffer waste is not required and handling procedures are minimized. This method (CASSOH-ELISA) has been successfully applied for the detection of clinically important SNPs in drug metabolism, such as N-acetyltransferase 2, NAT2*6 (590G>A) and NAT*7 (857G>A), and mitochondrial DNA (1555A>G). It would also facilitate point-of-care genetic testing for potentially diverse clinical applications.