Voiceprints, according to the author and to pioneer voiceprinter Lawrence Kersta, are as reliable as fingerprints in identification procedures. No two people have exactly the same voice. In voiceprinting, taped voices are scanned and turned into pictures by a spectrograph. Even David Frye's nimble Nixon imitation fails to beat the spectrograph. But the new technique is having its problems in court -- some convictions have been overturned either because the method seems too new and even subjective, or because a person is not required to testify against himself and some people feel that tapes violate the fifth Amendment. This last point is rebutted by the author who says that a voice is no more sacrosanct than a fingerprint. Block reviews several major cases (arson, extortion, murder, plane hijacking) in which voiceprinting was instrumental in reaching the truth, not necessarily in bringing about a conviction. (It has also been a factor in getting the accused off the hook.) Still not broadly accepted in the States, nor by Scotland Yard or Interpol, it is likely that voiceprinting will soon loom large in the law and that its day is not far off. It's fascinating to ponder its uses in divorce cases. . . .