Should the results of a lie detector test be considered solid evidence--like ballistics or fingerprints? Yes, say polygraph experts and many law enforcement personnel. No, says the ACLU and most courts which continue to follow an exclusionary policy. Block sketches the origin and development of the machine which monitors pulse, blood pressure, respiration, and galvanic skin response, and describes a number of sensational criminal investigations where the polygraph was used to clear the innocent and apprehend the guilty. (It's estimated at between 70 and 96% accurate.) But Block sidesteps the final verdict by stating that he will leave ""the question of polygraph credibility to the reader."" As to application--it ranges far beyond the criminal justice system. To the dismay of civil libertarians, the ingenious machine has been widely used by private industry and the federal government; Congress has introduced at least seven bills to prohibit use of the lie detector by the CIA, Defense Department, Postal Service, and other government agencies, despite pleas that the tests are needed to weed out subversives and other undesirables. For all Block's professed agnosticism, he sees the lie detector as an important instrument in ""providing justice to the accused""--though the proviso that the operator of the polygraph must be expert, unbiased, and proficient in the ""art"" of interpreting the data would seem to open the door to human error. By the author Of Fingerprinting and Voiceprinting, a further investigation into the science of police work.