Students culture mouse macrophage cells to confluence in a 6-well plate and then unleash these cells on cultured Escherichia coli bacteria. Three aspects of phagocytosis are examined: 1. Visualizing E. coli within the macrophage. 2. Determining how many bacteria are ingested by the macrophage cells. 3. Determining the number of bacteria still viable after a 1-hour exposure to the macrophages' lethal oxidative abilities. A simple quantitative methodology for evaluating host-microbe interaction is introduced. Assessment is a review of the student's laboratory notebook, questions in the handout, experimental results, and a brief laboratory report that integrates data analysis with discussion.