In the past fifteen years, the Ontario physician has witnessed a rapid and fundamental transformation in the political and economic context of his work. The imperfect market through which the delivery of medical services had been accomplished since the mid-nineteenth century has given way to an administered political economy. The decision by Canadian governments to establish programs of medical care insurance has entailed a series of challenges to the traditional institutions of medicine: to private, fee-for-service practice, and to professional licensing and disciplinary bodies. Issues not only of the economics and organization of individual physicians' practices, but also of the appropriate allocation of functions among health care personnel hav 5een placed on the political agenda. How can we expect physicians to respond to such a transformation of their work context? It has been popular in both the scholarly and the journalistic literature regarding physicians as political and economic actors to see them either as members of a powerful, cohesive, and collectively rational monopoly or as individually rational entrepreneurs. Each of these interpretations, however, is appropriate, if at all, to a particular stage in the transition from imperfect market to administered economy; and they are increasingly obsolete in the Canadian context. We shall suggest below that a concept of'corporate accommodation'is more appropriate to the understanding of the medical response in the later stages of the transition. But none of these models alone can comprehend the full range of medical political and economic behaviour and opinion. The speed of the transformation has meant that there exist within the Ontario profession attitudes and behaviour appropriate to various stages in the process, and that these different orientations coexist in considerable tension. There are fissures in what was once thought to be the monolith of medical opinion; and as the weight of government policy bears ever more heavily upon the profession, these fissures are becoming deeper and more apparent.