A novel technique was developed and verified for single nucleotide polymorphisms of human cytochrome P450 2C9 (*3 alleles) that affect the metabolism and clinical toxicity of drugs such as phenytoin, warfarin (Romkes et al)1. The detection system is split at a molecular level into signal-silent components. On hybridisation to their complementary target sequence, these components are assembled into a specific 3-dimensional structure, and can give an exciplex (Figure 1), which is detected by fluorescence spectroscopy (Bichenkova et al)2. Eight pairs of 12-mer oligonucleotide probes, labelled with pyrenyl or naphthyl exciplex partners at their 5′- or 3′- termini, respectively, were evaluated. Target DNA used in this study was in the form of short synthetic oligonucleotides (47 mer). The probes annealed to a complementary Wild Type oligonucleotide target and showed a characteristic exciplex fluorescence at 480 nm after excitation at 350 nm. This was accompanied by a quenching and slight red shift in the pyrene signal. With *3 SNP target oligonucleotide, exciplex signals of lower fluorescence intensity were detected, and there was a decrease in the Tm of the hybrid duplex by 1-2 °C. These results show that it is possible to use exciplex probes for detection of cytochrome P450 SNPs, with promise for future applications in genetic testing and molecular diagnostics.