To extend the understanding of the clinical problem-solving process, we have analyzed the tape-recorded behavior of experienced clinicians engaged in "taking the history of the present illness" from a simultated patient. We showed that specific diagnostic hypotheses were generated often with little more information than presenting complaints, that testing of diagnostic hypotheses consisted of various case-building strategies for corroborating and discrediting hypotheses, and that the process of information gathering included techniques to evaluate the validity of data and assess the need for immediate action. Overall strategies were more difficult to discern but included a focused approach, a systemic exploration method, and a chronologic technique. The data have potential value in medical education and in developing computer programs to simulate the diagnostic process.