The context of this discussion includes the application and support of chemical tests for alcohol statutes in the United States adversary system of justice. The goal of this review is to stimulate awareness among the various participants (that is, scientist, prosecutor, defense counsel, judges, and law enforcement officials) in traffic law enforcement situations. Their mutual understanding and cooperation is essential to the effective and efficient use of chemical test procedures. The relative scientific weight that should be given to blood, breath, and urine tests for alcohol is presented. (Author abstract)