A method for determining human mitochondrial aldehyde dehydrogenase (ALDH2) genotypes was developed. Two 21-base synthetic oligonucleotides, one complementary to the usual ALDH2(1) gene and the other complementary to the atypical ALDH2(2) gene, were used as specific probes for in-gel hybridization analysis of human genomic DNA from either peripheral blood cells or livers. Under appropriate hybridization conditions, these two probes can hybridize to their specific complementary alleles and thus allow the genotyping of the ALDH2 locus.