Helicobacter pylori is a Gram-negative bacterium that colonizes the gastric epithelium and plays a causative role in the development of peptic ulcers and gastric cancer. Phagocytosis is an element of innate defense used by macrophages and neutrophils to engulf microorganisms. We and others have shown that strains of H. pylori that contain the cag pathogenicity island actively retard their entry into phagocytes. Consequently, there is a lag of several minutes between bacterial binding and the onset of engulfment, and relative to other particles and microbes, the rate of internalization is slow. Herein, we describe in detail the use of synchronized phagocytosis and indirect immunofluorescence microscopy to quantify the rate and extent of H. pylori phagocytosis. This method is appropriate for primary phagocytes as well as transformed cell lines. More importantly, the effects of opsonins, virulence factors, and other agents on infection can be measured independent of bacterial viability or intracellular locale.