The instrument used was the Stop a Motorist Questionnaire (SMQ), which requires those who are tested to make discretionary judgments in a number of posited circumstances that invoke considerations of their status as a member of the police force, their relations with other ingroup members, and the need to deal effectively with both positive and negative public attitudes. The SMQ was administered at induction (Basic group) and after 1 year of service (Advanced group), both before and after training periods. Factor analysis showed a primary "in-group" factor before training, together with subsidiary "special cases" and "costs and benefits" factors, on all of which the Basic group was significantly more ready to take action. Factor analysis of the after-training responses showed that the primary factor was special cases, with subsidiary in-group and out-group factors. The Basic group was not significantly different from the Advanced group on the latter two but was still more likely to take action against special cases. The findings indicate that informal social and organizational encounters influence the exercise of police discretion, an impact that overlaps with and is as significant as any formal training strategy used by the organization. The value of the SMQ as an indicator of socially mediated change in police recruits has been confirmed, but within a limited context. 4 tables, 2 figures, and 50 references