The demonstration of the ability of exogenous cholecystokinin (CCK) to inhibit food intake began a series of investigations into whether and how gut and brain peptides affected ingestive behavior. In that original demonstration, Gerry Smith and colleagues both established criteria for evaluating roles for gut peptides in food intake and shifted the focus of feeding controls to factors that contribute to limiting meal size. Although new gut peptides with novel mechanisms and durations of action have been identified in the past few years, Smith's criteria and his distinction between direct and indirect controls of meal size continue to provide a framework for understanding how such peptides may contribute to overall feeding control.