THE STUDY of the relationship of hereditary factors to schizophrenia has stimulated a great deal of thought and research, as evidenced by the extensive literature on this subject. Until recently, the genetic methodology of workers in this field was primarily restricted to three proven, related, effective, but limited techniques. These were: (1) the use of careful geneological mapping; (2) statistical evaluation of large population groups to derive contingency and expectancy figures; and (3) the use of twin studies. Using these methods, investigators have derived concordance rates and expectancy figures that show a relatively stable trend, which indicates that the appearance of schizophrenia in a family is correlated with correspondingly elevated expectancy figures for its occurrence in other biologically-related family members.1-7 During the past decade the development of stable cytogenetic techniques, which allow for the actual observation and classification of human chromosomes, has