||The PDI assay kit provides a simple, homogenous assay for screening modulators of PDI enzymatic activity. This is accomplished by monitoring PDI-catalyzed reduction of insulin in the presence of Dithiothreitol (DTT), resulting in the formation of insulin aggregates which then bind avidly to the red-emitting fluorogenic ProteoStat PDI detection dye. Relative to analogous turbidimetric assays of PDI activity, the fluorescence-based assay provides a vastly improved assay signal window, improved lower detection limit, and superior Z"-score (>0.8). Intra-plate and inter-plate CVs using the assay are typically 3-5%. Human recombinant PDI enzyme (EC 18.104.22.168) and the PDI inhibitor, bacitracin, are included in the kit, as well as all reagents necessary for monitoring changes in PDI activity. The ProteoStat PDI assay kit is capable of providing a quantitative readout of PDI enzymatic activity in a robust and high-throughput fashion and can be applied to identification of PDI inhibitors from chemical libraries.