In 1974 a competency-based program was developed at the University of Arizona College of Medicine that used patient instructors (PIs) to evaluate interviewing skills objectively. PIs are nonphysicians who are taught to function in the multiple roles of patient, teacher, and evaluator. For each specialty area, objective evaluation instruments have been developed to measure the student's interviewing technique (interview process) and the amount of relevant historical information obtained from the patient (interview content). Data from the six most recent classes of second-year medical students demonstrate that: (a) there is a positive correlation between process and content scores; (b) students learn from their interviews with PIs; and (c) there is a positive relationship between the scores students obtain on their first interview with each of two different PIs in two different specialty areas. It is concluded that the PI program provides an effective way to teach interviewing skills to medical students.