Of particular concern in this area is the partition of alcohol among various bodily tissues and fluids and the resulting alcohol concentrations for blood, breath, and other body fluids, as well as the irregularity and short-term fluctuations of blood and breath alcohol curves. Most alcohol pharmacokinetic parameters are subject to wide intersubject variability. This variability, when combined with sex, age, and time-related differences makes blood-alcohol information based on mean data inappropriate as a guide to the drinking behavior of individuals. Further, while there is a good statistical correlation between tissue and fluid alcohol concentrations in the fully postabsorptive state, it is often impossible to determine if the postabsorptive state has been reached at any given time. These factors make it impossible or infeasible to convert urine or breath alcohol concentrations to the simultaneous blood alcohol concentration (BAC) with forensically acceptable certainty, especially under per se or absolute BAC laws. To remedy this situation, more research, using a more diverse subject pool and a standardized research protocol, is needed. There also is a need to develop legally acceptable and scientifically valid schemes for specifying BAC as an element in alcohol-related offenses. 72 references. (Author summary modified)