Student understanding regarding topics in upper-division courses, such as biochemistry, is not well represented in the literature. Herein we describe a study that investigated students' reasoning about Michaelis-Menten enzyme kinetics and enzyme inhibition. Our qualitative study involved semistructured interviews with fourteen second-year students enrolled in an introductory biochemistry course. During the interviews students were provided an enzyme kinetics graph, which they were prompted to describe. Students were asked to look for patterns and trends in the data and interpret the graph to draw conclusions regarding the types of enzyme inhibition observed, providing the opportunity for the students to engage in the science practice analyzing and interpreting data. Findings indicate students were able to attend to the relevant parameters (V[subscript max] and K[subscript m]) in the graph and subsequently associate changes in V[subscript max] and K[subscript m] to different types of enzyme inhibitors. However, students expressed difficulty explaining why a specific type of inhibition caused the observed change in the kinetic parameters and there was confusion regarding the distinction between noncompetitive and uncompetitive inhibition. Based on our results, we suggest instruction on enzyme kinetics should emphasize qualitative descriptions of the particulate-level mechanisms related to competitive and noncompetitive inhibition, with less emphasis on discussions of uncompetitive and mixed inhibition in introductory biochemistry courses.