The domination of the information processing approach has shifted research from problem solving strategies to the structure and organization of knowledge that characterizes expertise. The purpose of this study was to compare the reasoning processes of 12 clinicians and 40 medical students as they responded to 6 positively stated multiple choice items involving patient diagnosis. The theoretical framework that guided the study was the information processing theory of J. R. Anderson, which sees knowledge acquisition as a process in which individuals progress from novices to experts in sequential stages over a period of time. Clinician and student protocols were analyzed using subsets of behaviors related to the item stem and the choice options. The reasoning processes of the students and clinicians differed. While clinicians integrated the information presented in the stem and activated a hypothesis to explain all the information, students restated and focused on pieces of information in the stem, and used short connective links to relate one piece of information to an interpretation or possible answer. The differences in behavior appeared consistent with the Anderson information processing theory. Since students solve items by heeding the alternatives, each alternative presented should be integral to the central concept of the item and indicate a knowledge deficit or misconception. An appendix presents the multiple choice items. (Contains three tables and six references.) (SLD)