Cell signaling through the PD-1 receptor upon binding the PD-L1 ligand attenuates immune responses and is exploited by both tumors and viruses. The PD-1 PD-L1 (Biotin) Inhibitor Screening BioAssay™ Kit is designed for screening and profiling inhibitors of this signaling. This kit comes in a convenient 96-well format, with biotin-labeled PD-L1, purified PD-1, streptavidin-labeled HRP, and assay buffer for 96 binding reactions. The key to this kit is the high sensitivity of detection of biotin-labeled PD-L1 by streptavidin-HRP. Only a few simple steps on a microtiter plate are required for the assay. First, PD-1 is coated on a 96-well plate. Next, PD-L1 is incubated with PD-1 on the plate. Finally, the plate is treated with streptavidin-HRP followed by addition of an HRP substrate to produce chemiluminescence, which can then be measured using a chemiluminescence reader.