Abstract: The present invention relates to a method of detecting genetic variation in individuals by PCR amplification of the locus of interest, transferring the resulting PCR products to a membrane filter, hybridizing with allele-specific-oligonucleotides (ASOs), and visualizing the results. Such a method is in the field of diagnostics, pharmacogenetics, cancer therapeutics, and drug metabolism. In particular, the present invention relates to the detection of genetic polymorphisms in gene encoding xenobiotics metabolizing enzymes CYP1A1, CYP2D6, CYP3A4, and NAT2.