To provide objective and reliable evaluation of students' physical diagnosis skills, nonphysician patient instructors (PIs) with stable findings were trained by physicians to function in the multiple roles of patient, teacher, and evaluator. The PIs were taught physical examination techniques and the significance of each of their positive findings. Each second- and third-year medical student examined a cardiovascular and pulmonary PI. At the completion of each examination the PI evaluated the thoroughness and proficiency of the student's examination technique and ascertained whether the student correctly identified and described the abnormal findings. Objective and reliable evaluation instruments were developed. Data are presented to indicate that PIs can be used to evaluate objectively physical diagnosis skills of medical students.