During the twentieth century, episodes of major health policy reform were relatively rare. These rare episodes were pivotal ‘critical junctures’ in determining the paths taken by modern health systems and in creating a unique health policy arena. A pivotal ‘turning point’ in Australia came in the form of national health insurance. Introduced in the early 1970s, Medibank (universal, compulsory national health insurance) was the first significant structural health policy change in Australia during the twentieth century. When Medibank health insurance proposals were presented in Australia, political struggles erupted. Government leaders in Australia faced fierce opposition from key players within the health policy arena. Prior to this turning point, one of the key health policy players—the Australian Medical Association (AMA)—had developed a corporate partnership with the non-Labor government. When the Medibank proposal emerged, power structures in the health policy arena were re-aligned. The political role of the AMA shifted from a corporate partner to a pressure group. Examining the political processes surrounding this unique episode of major health policy change helps to illuminate the dual and dynamic nature of the doctors’ lobby. Our study aims to demonstrate empirically Day and Klein's proposition that the doctors’ lobby operates as a pressure group, rather than as a corporate-style partner, during periods of structural reform in health care [ Political Studies, 40 (1992) 462]. This case study of the doctors’ lobby during Medibank negotiations represents a rare break in the tradition of ultimate medical professional veto power in health policy decision-making and provides empirical evidence that challenges a widely held perception about an inevitable historical path of medical dominance.