The Precursors Study is a long-term prospective investigation of the characteristics of a cohort of 1,337 Johns Hopkins medical students, in classes graduating in 1948 through 1964, to determine youthful predictors of premature disease or death. Now for the most part physicians aged 40 to 59, their health and that of their parents are being followed annually by mail. By 1977, over 200 subjects had been affected by one or more major disorders. Studies to date, on data obtained from individuals while they were medical students, have identified a number of specific, separate characteristics which distinguish between subjects who remain healthy and those who have died prematurely or become diseased, and between subjects with one form of disorder and those with another. These separate items represent four different categories of data: Biological (e.g., mother's age at subjects' birth); Physiological (e.g., resting diastolic pressure, resting heart rate); Metabolic (e.g., relative body weight, cholesterol level); and Psychological (e.g., depression, anxiety and anger under stress, closeness to parents, family demonstrativity, pathological unconscious psychic processes and content). The aim of future studies is to go beyond the present listing or aggregation of separate characteristics, and to organize material in the data base in such a way as to portray the individual as a biological-cultural organism with a characteristic core, a long-range style in experiencing, shaping and adapting to his successive life events. The time span since the original data were collected is now 14 to 30 years, so much added data have accumulated on the life styles and life events of both healthy and unhealthy subjects.