The guide and an explanatory booklet were developed to aid officers in identifying the visual cues of drunken drivers. The guide was a small card of white plastic listing major cues and the probability that a nightime driver with a blood-alcohol content (BAC) equal to or greater than 0.10 would exhibit them. The field test -- conducted at 10 law enforcement agencies throughout the country -- was designed to provide both longitudinal and cross-sectional analyses of several measures likely to reflect the impact and utility of using the guide and to verify the values contained in it. Use of the guide was accompanied by a statistically significant overall increase in the DWI arrest rate of 12 percent. Rates during a 3-month period, in which the guide was used, were compared to a 12-month baseline period. Five individual agencies had significant arrest increases of up to 94 percent; four agencies had no change; and one had a significant decrease. Although no statistically significant changes in detection practices were reflected by greater use of the more discriminating cues or by arrests of drivers with lower BAC levels, trends were in those directions. Experienced police officers who used the guide expressed doubts about its value in improving their own DWI enforcement ability; however, they considered the guide to be valuable for increasing patrol sensitivity to important cues, training new officers, preparing DWI arrest reports, and supporting court testimony. Field test results led to minor modification in the guide. Footnotes, a summary of the guide development phase of the project and data tables are included. The guide and booklet are appended.