The efficiency of the Guilty Knowledge Test was assessed when the polygraph examiner was aware of some of the crime- relevant items, target items (items significant to participants for reasons other than crime relevance) were incorporated in the test, and motivation of guilty participants to appear innocent was manipulated. Experimental participants included 80 Israeli males who ranged in age from 19 to 51 years. The experiment was conducted in the police polygraph laboratory. The mock crime design involved one group of 25 participants who acted out the mock crime and 55 participants in another group who simulated innocents. Results showed that participants yielded weaker responses to relevant items when the polygraph examiner was aware of them than when the polygraph examiner did not have this knowledge. The inclusion of target items had no overall effect on responses to relevant items, highly motivated participants within the guilty condition were more responsive to relevant items than less motivated participants, and the inclusion of target items significantly decreased the detection accuracy of low-motivated participants. 21 references and 4 tables