The effects of simple physical countermeasures on the validity of the control question test (CQT). a physiological detection of deception (PDD) technique. was investigated in a laboratory mock criae paradigm. Forty-eight Introductory Psychology students served as subjects and were assigned to either an innocent group or to one of three guilty groups. who participated in a mock crime. Two of the guilty groups were trained in a countermeasure technique, either self-induced pain or muscle tension, and were coached as to when to produce responses in order to beat the test. All subjects were motivated to produce truthful responses by the offer of credit points toward their final grades if they were classified as truthful on a subsequent PDD examination. All subjects were given a field type CQT examination by an experienced field PDD examiner. The examiner correctly classified 52% of the subjects, incorrectly classified 61% and called 42% inconclusive. Countermeasure usage did not produce changes in the frequency of either inconclusive of incorrect classifications. Statistically significant differences were found between the innocent and guilty groups in the semi-objective scores and in all of the objectively reduced measures (except heart rate). A significant but small difference was found between the guilty control and the countermeasures groups in finger pulse amplitude but in no other objective measure nor in the semi-objective scores. These results suggest the validity of the CQT to be robust in the face of the countermeasures used. Implications for field use of the CQT were discussed. / M. S.