An assessment technique was developed to measure the abilities of medical students to deal with moral and ethical issues. Assessments of ability in moral reasoning and ethical judgement were administered in July and August of 1991 and 1992 to 511 fourth-year students from five northeastern U.S. medical schools. Five behavioral parameters were measured during each student's encounter with a standardized patient (SP), who graded the student's performance. Immediately following the encounter, each student was asked to describe at least two moral conflicts in a short essay, which was graded by the authors of the study. Statistical analysis used chi-square, Fisher's exact test, and Spearman rank correlation. Poor performance on the interactive tasks with the SP was observed among 11% of the students; on the written (analytical) tasks, among 14.1%; and on both portions of the assessment, among 2.3%. Little relationship existed between performances on the interactive and written portions. That a low degree of relationship was found between the students' performances on the interactive and written portions of the assessment suggests that the two portions measure different skills. To address student differences, the authors formulated a model for categorizing students that would be useful in individualizing remedial strategies.