Trypsin and soybean trypsin inhibitor (Kunitz inhibitor) can be used in a relatively simple and inexpensive student exercise to demonstrate the usefulness of enzyme kinetics. The study of enzyme kinetics is essential to biology because enzymes play such a crucial role in the biochemical pathways of all living organisms. The data from enzyme kinetics experiments not only reveal the mechanisms and limits of enzyme-catalyzed reactions, but also provide insights on how to manipulate these reactions. Numerous laboratory exercises exist in which students learn how to perform enzyme kinetics experiments and calculate the numerical parameters describing enzyme efficiency. However, it is often difficult to persuade students of the importance and relevance of their enzyme kinetics data. The purpose of this student exercise is to convince college students in Introductory Cell Biology that the ability to understand and calculate the values that describe enzyme activity is worthwhile and has concrete applications. Although designed for college laboratories, ways to adapt this experiment to high school classes are included. (Contains 3 figures and 3 tables.)