A sample of 186 officers was questioned at the beginning and end of a 1-year period with respect to their attitudes toward OUI (Operating Under the Influence of Alcohol) law enforcement and their discretionary behavior in regard to OUI. Significant minorities of police officers reported that they made decisions either not to apprehend (33-percent) or not to arrest (41-percent) OUI suspects in the study year. Officers who reported discretionary decisions not to apprehend or arrest generally did so infrequently -- i.e., 5 percent of possible apprehensions and 10 percent of possible arrests. Type of police department was significantly associated with decisions not to stop OUI suspects: officers in large departments (greater than or equal to 20 officers) reported more discretion. Officers with longer service careers, administration responsibilities, high personal priorities on OUI enforcement, and favorable opinions of the climate of OUI enforcement were less likely not to arrest OUI suspects. (Author abstract)