This volume contains the proceedings of the fourth international symposium held in November 1970 at the Texas Research Institute of Mental Sciences in Houston. Leading psychiatrists, biochemists, and pharmacologists from the United States and Great Britain presented new material and reviewed current concepts concerning schizophrenia and the affective disorders, with particular reference to the neurochemical basis of the etiology and chemotherapy of these diseases. Although the multiple mechanisms of mental disease are still not fully understood, substantial progress has definitely been made. The greatest contribution has come through the development of new therapeutic agents that not only provide invaluable help to the mentally ill but serve as chemical tools for studying the biological mechanisms associated with the disease state. Studies concerning the proposed catecholamine and indolealkylamine hypotheses for affective disorders and the possible formation of endogenous. toxins in schizophrenia have stimulated significant new research. This book presents new studies of schizophrenia and the affective disorders in one volume. It is our hope that it represents an effective integration of basic biochemical and pharmacological research with current clinical findings and that it will increase understanding of the etiology of mental disease and provide an impetus for the development of more effective therapeutic agents. We thank Drs. Gordon Farrell, Samuel Gershon, A. Horita, Irwin Kopin, and Joseph Schildkraut for their help with the organization of the meeting and for chairing the corresponding sessions.