To establish whether some physicians contribute more than others to the alarming increase in laboratory related expenditure, 317 consecutive medical files established by 10 residents of an outpatient clinic were analyzed. The expense incurred in establishing a diagnosis varied, according to the physicians involved, by a factor of 4.9 for back pain and 2.6 for acute respiratory illness. The difference is even more striking when the various types of investigation are analyzed (blood count, ESR, X-rays). It is therefore possible to group physicians according to their individual tendency to order tests. This classification is not related to age, sex, former professional experience or sub-specialty in internal medicine. There is a significant correlation (Spearman's test) between this classification and the approach to medicine, as evidenced by analysis of the content of an interview on medical practice. These interviews were conducted double blind, recorded and transcribed to determine psychological traits. Physicians who order a large number of tests are characterized by a high index of uncertainty, as evidenced by the large number of hesitant expressions and a tendency to cut the interview short, showing off to compensate for lack of self-assurance, depersonalized reference to patients, few references to the interviewer, difficulty in establishing a true dialogue. These characteristics can be considered to form a coherent entity which shows that even the material aspects of medical practice are strongly influenced by the physician-patient relationship.