Many countries are importing managed care and price competition from the US to improve the performance of their health care systems. However, relatively little is known about how power is organized and exercised in the US health care system to control costs, improve quality and achieve other objectives. To close this knowledge gap, we applied social exchange theory to examine the power relations between purchasers, managed care organizations, providers and patients in the US health care system at three interrelated levels: (1) exchanges between purchasers and managed care organizations (MCOs); (2) exchanges between MCOs and physicians; and (3) exchanges between physicians and patients. The theory and evidence indicated that imbalanced exchange, or dependence, at all levels prompts behavior to move the exchange toward power balance. Collective action is a common strategy at all levels for reducing dependence and therefore, increasing power in exchange relations. The theoretical and research implications of exchange theory for the comparative study of health care systems are discussed.