Examining the epidemiological literature, a relationship between physical activity and the development of NIDDM seems not only plausible but likely. What is needed is a randomized clinical trial to confirm the metabolic and epidemiological research findings to date. To maximize success of a diabetes prevention trial, both diet and physical activity should be part of the intervention. The relative importance of diet or physical activity as components of the intervention will vary, depending upon the participant. However, it is critical that compliance with the physical activity and diet intervention be maintained, for this question to be answered. If the intervention is successful, the participants will have made lifestyle changes that have the potential of lasting beyond the closure of the clinical trial.