Increasing levels of physical activity are associated with a decrease in cardiovascular events. Controlled clinical trials suggest that exercise has benefits in persons with coronary artery disease and in those with glucose intolerance.¹ Exercise produces improvements in mood, blood pressure, insulin sensitivity, and plasma lipoprotein profiles, but the amount and intensity of exercise required in order to attain these benefits and the underlying mechanisms are poorly understood. In this issue of the Journal, Kraus et al.² report on changes in plasma lipoprotein levels and particle sizes in an eight-month, randomized trial involving different amounts and intensities of exercise among overweight . . .