Phagocytosis provides a first line of host defense against potential pathogens and is used as a model of microbe-innate immune interactions, resulting in increased understanding of the consequences of these interactions. Phagocytosis involves a complex series of events including cytoskeletal rearrangement, alterations in membrane trafficking, activation of microbial killing mechanisms, production of pro- and anti-inflammatory cytokines and chemokines, activation of apoptosis, and production of molecules required for efficient antigen presentation to the adaptive immune system. Of the variety of assays available to study the regulation and mechanism of phagocytosis in vitro, the flow cytometric assay has an advantage of rapid analysis of thousands of cells and quantification of internalized particle density for each analyzed cell. Cayman's Phagocytosis Assay Kit (IgG PE) employs latex beads coated with phycoerythrin (PE)-labeled rabbit-IgG as a probe for the identification of factors regulating the phagocytic process in vitro. The engulfed fluorescent-beads can be detected using a microscope or plate reader capable of measuring excitation and emission at 494 and 578 nm, respectively, or be analyzed by a flow cytometer capable of excitation at 488 nm.