The survey instrument used in the national study of physician activities conducted by the University of Southern California, Division of Research in Medical Education, is a log-diary in which physicians kept a record of their actual professional activities. The log-diary focused on use of physician time and patient encounters and employed numerical coding of activities and patient encounters in a highly structured format. Compared with instruments used in similar studies, this log-diary appears to gather a greater breadth and depth of information about physician practice patterns.