tumor-suppressor gene FHIT is one candidate. The gene product, FHIT protein, has a unique dinucleoside triphosphate hydrolase (AP3Aase) activity, and in this study, we designed and synthesized a series of FHIT fluorescentprobes utilizing this activity. We optimized the probe structure for high and specific reactivity with FHIT and applied the optimized probe in a screening assay for FHIT inhibitors. Screening of