The disjunction between scientific and judicial standards of evidence has allowed novel forensic methods to be used in criminal trials prematurely or without verification. The problem has become particularly apparent in the case of forensic DNA profiling. Although many aspects of forensic DNA identification have not been adequately examined by the scientific community, police and prosecutors have carried out DNA analysis in more than 1,000 criminal investigations in the United States since 1987. The ongoing debate over DNA testing underscores the need to deal more effectively with difficulties associated with introducing complex scientific evidence in courts of law. To be admitted as evidence, a forensic test should satisfy three criteria: the underlying scientific theory must be considered valid by the scientific community; the technique itself must be reliable; and the technique must be properly applied in the particular case. In addition, in order for courts to evaluate forensic evidence, judges and lawyers must be able to understand the scientific issues involved. Lawyers, however, rarely do more than review the qualifications of the expert and verify the facts on which the expert's conclusions are based. The problem of scientific illiteracy is compounded by the tendency of judges to refuse to reconsider the validity of a particular kind of scientific evidence once it has been accepted by another judge in an earlier case. Because defendants are seldom able to challenge novel scientific evidence, the authors believe that independent oversight of forensic methods is the only way to ensure justice. Specifically, national standards must be set before a scientific technique can be transferred from the research laboratory to the courtroom. References and figures