A study investigated the known phenomenon of "intermediate effect" in which medical students with an intermediate amount of knowledge and experience demonstrate higher amounts of recall of the text of a medical case than either experienced clinicians or novices. In this study the amount of activation of prior knowledge was controlled by having subjects--24 fourth- and 24 sixth-year medical students at the University of Limburg (Netherlands) and 6 internists--spend either 30 seconds or 3.5 minutes recalling whatever they knew about endocarditis before being presented with an endocarditis case to comprehend and recall. Findings indicated that the more time subjects had available the more knowledge about the subject they were able to produce; that the amount of prior knowledge produced is a function of level of expertise (physicians produced more information than students); but that "experts" (physicians and sixth-year students) recalled less information but more relevant information about the case than did intermediates (fourth-year students). The results supported the theory that experienced physicians develop cognitive structures or "illness scripts" which they use to automatically represent a case. Contains 14 references. (DB)