This analysis of field data from 1991 and 1992 examines the process of joint decision making between cardiothoracic surgeons and anesthesiologists in a U.S. hospital as they made changes in clinical practice in response to reimbursement reductions. Although these physicians have concurrent responsibility for patient care in the operating room, their domains of authority are ambiguous. Much clinical decision making was found to be based on charismatic authority. In making practice changes, cardiothoracic surgeons maintained all and anesthesiologists most of their charismatic authority, expanding the conventional range of physician practice while prescribing specific practices for nonphysician providers. Ambiguity of joint physician authority over patient care was left unresolved, and the economic goals of the practice changes were not realized. Physicians resisted the bureaucratic claim to authority rooted in cost accounting by resorting to the need for nonroutinized clinical decisions.