We used measures of regional brain electrical activity to show that not all smiles are the same. Only one form of smiling produced the physiological pattern associated with enjoyment. Our finding helps to explain why investigators who treated all smiles as the same found smiles to be ubiquitous, occurring when people are unhappy as well as happy. Also, our finding that voluntarily making two different kinds of smiles generated the same two patterns of regional brain activity as was found when these smiles occur involuntarily suggests that it is possible to generate deliberately some of the physiological change which occurs during spontaneous positive affect.