Arguing from genetic, clinical and statistical evidence it is concluded that there is little support for the traditional view of the schizophrenias as qualitatively distinct diseases. A view more consistent with available facts is that they represent, in an exaggerated form, cognitive and personality characteristics found distributed among the general population. Starting from this dimensional view it is further argued that the predisposition to schizophrenia, like other personality dimensions, has a discoverable psychophysiological basis, in the form of a particular kind of nervous typological organization. The two most important processes involved seem to be those of arousal and attention, and evidence is reviewed in support of the author's theory that it is the manner in which these two processes co-vary that is uniquely different in schizophrenics and in normal individuals highly predisposed to schizophrenia. The special importance of drug techniques as nervous typological tools is emphasized and illustrated with some recent experimental findings on LSD-25. It is concluded that research such as that described may eventually lead to the development of pharmacological procedures which can identify individuals who are psychophysiologically predisposed to schizophrenic breakdown under stress.