Enzo Life Sciences’ ProteoStat™ 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 5.3.4.1) 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.