Sir-Large-scale screening for known polymorphisms will require techniques with a minimal number of steps and the ability to automate each one. In this regard, the 5'nuclease PCR assay first described by Holland et a [. 1.2 and refined by Lee et aP is especially attractive because it virtually eliminates post-PCR processing. For this assay, a fluorogenic probe, labelled with both a fluorescent reporter dye and a quencher dye, is included in a typical PCR amplification. During PCR, this probe is cleaved by the 5'nuclease activity of Taqpolymerase1• 4, onlyifit hybridizes to the segment being amplified. Cleavage of the probe generates an increase in the fluorescence intensity of the reporter dye. Thus, amplification of a specific product is detected by simplx measuring fluorescence after PCR. Furthermore, by using different reporter dyes, cleavage of multiple probes can be detected in a single PCR. Lee et aP used probes labelled with the reporter dyes F AM and TET to distinguish the M508andnormalallelesofthehuman cystic fibrosis gene. The-23 A/T diallelic polymorphism of the human insulin gene (INS) is associated with susceptibility