Psychosocial characteristics that identified first-year medical students who drank more or less alcohol than their peers were examined. Subjects were 116 freshman medical students (96% of one class) who completed questionnaires about alcohol use, mood, personality, social relationships, and parental alcohol abuse on the first day of school, and 106 (88% of the class) who responded to the same questionnaires in April of the first year. Heavier drinking students (i.e., the upper 25% of the sample) were more likely to be male and single, to have drunk heavily prior to medical school, to come from larger social networks which include fewer relatives, and to demonstrate a lower interpersonal orientation. Mood, academic performance, and parental alcohol abuse were not associated with drinking level. The heaviest drinkers in this sample appear to be precisely those individuals who are most impervious to peer or other social influences. [ABSTRACT FROM AUTHOR]