IncuCyte® Rat FabFluor pH Red Fluorescent Reagent utilizes a novel pH-sensitive dye coupled antibody fragment, which labels Fc-containing rat test antibodies and allows for rapid antibody internalization and kinetic high-throughput analysis. The FabFluor reagent is specifically formulated for use in the IncuCyte ® live-cell analysis system and can be added directly to tissue culture wells using a no wash, simple mix and read protocol to acquire live cell images of adherent and non-adherent cells. When labeled antibodies are added to cells, a fluorogenic signal is quickly observed as the Fab-Ab complex is internalized and processed via acidic lyosomes and endosomes. Antibody Internalization can then be monitored using live cell imaging, and quantified using IncuCyte® software and analysis system. This method can be easily scaled up to compare uptake of hundreds of antibodies in parallel to answer key questions around antibody selection and optimization for biologics drug discovery.