The primary difficulty in lie detection is the absence of a unique, identifiable physiological response associated with truthfulness or deception. Subjects have their own autonomic response potential. Each subject's particular autonomic response potential is determined with the use of control questions. The control question must be a lie or be difficult to answer truthfully so as to elicit the same emotional states which will be potentially elicited in the subject's responses to the questions relevant to the target incident. Also, the control question must present a threat to the truthful subject's goal orientation, so the control question should deal with an issue similar to the subject's perception of the issue under investigation. The control question must be broad so as to increase the likelihood the subject will have difficulty answering it truthfully, and the control question should be formulated and reviewed in consultation with the subject. The latter is necessary to determine whether the control question is being perceived properly and whether the subject is having difficulty answering the question truthfully. 23 references.