The members of the medical profession are heavily dependent on a set of formal institutions and informal organizations. In an eastern American city here reported the established specialists constituted the inner core of the profession. This core functioned to control appointments to the medical institutions, to exclude or penalize intruders, to distribute patients, and to enforce rules and control competition. The influence of this inner core is crucially important in the careers of new recruits to medicine. The stages of a medical career are here set forth as a set of adjustments to this inner core and to the institutions it influences.