Chronically-ill nonphysician patient instructors (PIs) with stable cardiovascular or pulmonary findings were trained by physicians to evaluate objectively the physical diagnosis skills offirst-year house- officers (PGY-1s). Each PGY-1 received a performance score, reflecting thoroughness of examination, and a content score, reflecting ability to identify and describe findings. There was no significant correlation between performance and content scores in either specialty or between scores obtained on the two specialty examinations. Scores for the PI evaluations were correlated with traditional assessment methods. Evaluation of PGY-1s by program directors correlated positively with performance scores; peer ratings correlated positively with content scores. Internship acceptance committee rankings correlated positively with cardiovascular content scores and peer evaluations. The use of PIs to evaluate physical diagnosis skills of PGY-1s provides numerical objective data not previously available from any other single source.