To examine the characteristics of expertise, a study at the University of Minnesota cardiac clinic compared differences in diagnostic ability and strategies between novices (fourth year medical students) and experts (specialists in pediatric cardiology). The investigator presented a model for expertise based on knowledge of subject matter content and knowledge of reasoning procedures. Four medical students and four specialists diagnosed eight cases, four in a simulated clinic task and four in a consultant task. All sessions were audiotaped. The novices and experts made different diagnoses based on a varying knowledge of the subject matter content and the use of different reasoning procedures. For example, a student used the procedure of successive scanning (considering only one hypothesis at a time) when he was reasonably sure of his diagnosis, while a specialist used a focusing strategy (reducing the set of hypotheses already generated) to limit the possibilities. The conceptualization of expertise as a combination of knowledge of content and knowledge of procedures is particularly relevant to the adult educator. Since most adults have mastered general strategies of learning, they need to learn and apply the procedures unique to an area in order to develop expertise in that area. A careful investigation of the expert's strategies can be utilized for programs designed to develop that expertise. A bibliography and diagrams related to the study are included in the report. (LMS)