While noting that there is no international scientific or legislative uniformity in blood alcohol concentration (BAC) levels admissible for driving motor vehicles, the authors analyse problems concerning the effects of low levels of ethyl alcohol on driving ability. A summary of the international literature on this subject reveals: the existence of contrasting assumptions, with scientific evidence clearly demonstrating altered psychomotor functions; the need to adopt sufficiently complex psychometric tests to reveal the effects of low BACs; the need to improve standardization of experimental studies on man-machine interaction; the need to investigate the following areas: tolerance to alcohol; low BACs with inexperienced, infrequent drinkers and chronic, heavy drinkers; hangover effects; alcohol-gender-age interactions, and specific effects on young drivers; alcohol-drug combinations. The analysis of legislation and enforcement policies also reveals the need for: re-evaluation of the international legal BAC threshold and standardization of procedures for ascertaining the degree of driving disability; further scientific research to compare and evaluate selected legislative initiatives currently in place in most states; to identify the best strategies and procedures to detect and arrest impaired drivers; to determine the optimum random testing rate to maximize deterrent effects in the workplace at minimal cost; to design innovative and comprehensive approaches to rehabilitation programs needed for subgroups of offenders and of workers; to study the effectiveness of new legislations and policies.