Supervisory behaviors considered effective by medical students were identified and organized into descriptive categories. A second study objective was to compare the supervisory behaviors of family physicians and those of behavioral scientists. Eighty-four sophomore medical students completed a critical incident report form at the end of an interviewing practicum session during which they were co-supervised, in groups of four, by a family physician and behavioral scientists. Working independently, 11 judges sorted the reports of effective and ineffective supervision behavior by physicians and behavioral scientists into 11 categories. Using joint proportion matrices and principal component analysis, source variables underlying the observed behaviors were identified. The requirements for effective supervision by physicians were to model the physician's role, teach clinical problem solving, provide balanced feedback, suggest how to improve interviews, structure the task, prod critical thinking, and confront defensiveness. The supervision requirements for behavioral scientists were to teach interviewing and interpersonal skills, provide constructive criticism, discuss patient behavior, convey personal support, promote change, and facilitate group interaction. (Author/SW)