Physical evidence plays a significant role in the criminal justice system. However, not only can physical evidence answer many legal questions surrounding a crime scene, it can also influence the processing of defendants through the system, accompanied by effects that are not always intended or desired. Some of the key concerns are the extent to which courts will allow the forcible (nonconsensual) taking of physical evidence (hair, blood, etc.) from a suspect and applicable search warrant requirements, if any. Perhaps one of the major legal and procedural issues involving DNA testing is whether it will inform the trier of fact. Related to this is whether expert witnesses presenting DNA evidence will overwhelm a jury with statistical arguments. And, finally, whether it will clarify questions surrounding guilt or innocence or merely serve to further confuse the decision making process. The article concludes that, for DNA evidence to be widely accepted, access to laboratory analyses and expert witnesses may be as important as admissibility. And, as intrusiveness of the process increases, the courts may require increased levels of proof, such as probable cause. Notes, references