Forty-five subjects enrolled in criminal justice classes in a northwestern university participated in this 3-phase study. In the first phase, the subjects completed the Harvard Group Scale of Hypnotic Susceptibility: Form A. During the second phase, 15 subjects were randomly assigned to each of three groups controlling for their levels of hypnotic susceptibility: the countermeasure (CM) condition, the ideomotor condition (CM), or the control group. In the CM condition, the subjects were given a posthypnotic countermeasure designed to help them appear innocent whenever they lied; in the IM condition, the subjects were given the posthypnotic suggestion that the subjects index finger would rise whenever he or she lied during the polygraph test. None of the subjects given the IM suggestion raised his or her finger when he or she lied during the polygraph test. The CM suggestion was equally ineffective as demonstrated by its failure to produce significantly false negative responses. 5 tables and 41 references (Author abstract modified)