Subjects enacted or did not enact a mock crime and then were given a control question test using standard polygraph techniques. Subjects were offered a cash reward for a truthful outcome on the polygraph test. Of the guilty subjects, 60 percent reported using mental or physical countermeasures to defeat the test. The most frequently used tactics were relaxation and attempts to control breathing. Independent evaluators' diagnoses of truth and deception were 80 percent correct, 3 percent incorrect, and 17 percent inconclusive. Additional analysis failed to show any effects of the use of countermeasures on test outcomes. Results suggest that spontaneously attempted countermeasures are not effective in defeating control question polygraph examinations. That the experienced polygraph examiners in these studies were unable to detect the use of spontaneous countermeasures suggests that training in this area is needed. 2 tables and 13 references.