In the 1960's several studies were carried out that pointed toward a significant genetic contribution in the development of schizophrenic illness. S. Kety, D. Rosenthal, and P. Wender's studies of adoptees in Denmark played an instrumental role in widening the concept of schizophrenia so that it came to encompass a spectrum of disorders, including so-called "borderline schizophrenia." They described evidence of genetic influences in "borderline" as well as in more typical schizophrenic illnesses. Because of the work of these and other investigators, there has been a burgeoning interest in biological