The assessment was conducted in four phases. The core of this research revolved around providing PBT devices to 101 Missouri State Highway Patrol road officers who had shown a high proficiency in making DWI arrests. The first phase of the study coincided with the field test and consisted of monitoring PBT device usage and DWI arrest levels of field-test participants. The study's second phase solicited participants' opinions about the use of the instrument and its effectiveness in DWI enforcement. In the study's third phase, participants reported the evidential breath-test results in all DWI arrests made in 1994. In the study's final phase, a number of State Police information systems were accessed to obtain 1994 data related to the number of DWI arrests made by field participants, the number of traffic crashes they investigated, and the amount of time they expended on proactive patrol. Overall, the findings show that the PBT devices can significantly aid the law enforcement community in detecting and arresting intoxicated drinking drivers. 17 tables and sample study instruments