The technique of DNA identification compares the DNA of two samples of body tissue to determine whether or not they came from the same human being. The comparison of human DNA molecules does not require the analysis of the entire DNA molecule, only the portion of the human DNA that is sufficiently variable to be unique to individuals. The most important use of DNA identification by crime investigators is to compare a profile believed to be from a crime perpetrator with a known person's profile. The presentation of DNA identification evidence in a criminal trial can be difficult for a number of reasons. First, DNA identification evidence consists of a number of facts, including the circumstance in which the relevant body samples were obtained, their secure transportation to a laboratory, their analysis, and the detection and recording of DNA profiles. Second, evidence law requires opinions about forensic interpretation to be presented by a person with specialized knowledge based on training, study, or experience that substantially or wholly supports the opinion. When people have been wrongly convicted, exculpatory DNA evidence may form the basis for an appeal against conviction. The costs of increased reliance on DNA technology in criminal investigations include not only the obvious financial costs of scientific expertise, laboratory equipment, and the administration of information databases, but also the unquantifiable costs of a possible reduction in individual freedoms, notably the right to privacy, and the right against self-incrimination. 3 tables and 35 references