Flow cytometry has become an important tool in the life sciences and medical fields, yet there are often few opportunities for undergraduate students to receive training with this type of instrumentation as part of life science curricula at many colleges and universities. We describe a straightforward laboratory exercise designed for a college-level biochemistry course that uses flow cytometry to investigate changes in bacterial membrane potential and cell viability in response to various treatments. Anecdotally, we have noticed that many students often have difficulty understanding the concept of membrane potential and the essential role that it plays in cellular processes. Therefore, this exercise also provides a pedagogical tool for visualizing changes in cellular membrane potential as way to enhancing students' comprehension of this abstract concept. Students' understanding of flow cytometry and membrane potential was assessed using a preactivity and postactivity quiz; the results indicate that the students' understanding of these concepts significantly improved after they completed this laboratory exercise.