This report presents a general framework for studying the acquisition and cognitive representation of biomedical concepts and analyzing the nature and development of misconceptions. The central approach of the report is a selective and highly concentrated analysis of the true nature of clusters of complex concepts and the manner in which they are understood by learners. The report finds a widespread tendency for medical students to develop significant errors in conceptual understanding, including specific conceptual misunderstandings and maladaptive biases in the thought processes used in dealing with complex concepts. The report notes particularly the tendency for misconceptions to compound each other within a general climate of oversimplification, producing large areas of entrenched misunderstanding. The report considers in detail the factors contributing to the acquisition and maintenance of the fallacy concerning the causal basis of congestive heart failure at the level of the muscle cell. The report concludes with a discussion of the implications of the findings for learning and instruction. (Nineteen figures are included, and 39 references and 6 footnotes are appended.) (Author/RS)