This paper discusses the processes that determine the characteristics of professional sub-cultures. It was postulated that mechanisms of attraction, formal and informal selection, promotion and reinforcement of desired characteristics serve to shape the personality which characterizes the members of a profession and can be expected to result in a common set of values, attitudes and skills. It was also postulated that these mechanisms could be investigated through use of self descriptions which identify the common beliefs, typical behaviors, preferences, and values of members of the profession. The Job Analysis and Interest Measurement (JAIM) was administered to beginning students at schools preparing candidates for five professions: social work, law, public administration, business administration, and army officer. The JAIM was again administered at the end of training to social work students and army officer candidates. Results supported the major hypotheses. Highly significant differences were found (1) among student groups preparing for different professions, (2) among students expressing preferences for different sub-specialties, (3) between students who dropped out of training and those who stayed, and (4) between scores for students obtained at the beginning and at the end of training. (AF)