Trends in Europe and North America, analysis of alcohol in body fluids, pharmacokinetics of alcohol in blood and breath, alcohol tolerance and individual variations, and alcohol in blood and breath as evidence of impairment are discussed. The use of punishable blood alcohol content (BAC) limits as an effective countermeasure to driver behavior under the influence of alcohol is discussed. Most developed nations enforce drinking and driving laws that rely on a definition of impairment in terms of the concentration of alcohol in the motorist's blood (BAC). Two basically different drink-driving statutes are in effect: (I) illegal per se limits of alcohol concentration in a specimen of blood, breath, or urine, and (II) presumptive laws that merely presume guilt if the result of analysis is above the prescribed legal limit. An important distinction stems from the fact that presumptive laws are rebuttable whereas per se statutes are not (Ziporvn, 1985). In practice, illegal per se laws are easier to enforce because they offer a clearcut definition of when an individual is breaking the law. The result of forensic analysis therefore becomes the sole deciding factor needed as evidence to gain a conviction. 4 figures and references. (Author abstract modified).