A quantified electrophysiological system called Neurometrics is described in terms of procedures, reliability and validity. The role of the computer in both acquisition and analysis is noted. In terms of the application of Neurometrics to issues of diagnostic validity five studies are discussed. The first describes a study showing that normal functioning and at risk children differ markedly in terms of the percentage showing EEG abnormalities; the second reports the difference between children who are poor achievers in verbal, arithmetic or both skills; the third shows that Neurometric indices differentiate between epileptic children who are achieving or not achieving at grade appropriate levels; the fourth describes Neurometric EEG differences between learning disabled children who do or do not have reading reversal problems; and the fifth describes the behavioral differences constructed on the basis of their Neurometric profiles.