Received March 10, 1997; revision received Oct. 7, 1997; accepted Oct. 13, 1997. From the Department of Psychiatry and the Department of Radiology, New York University Medical Center, and the Department of Chemistry, Brookhaven National Laboratory, Upton, N.Y. Address reprint requests to Dr. Brodie, Department of Psychiatry, New York University Medical Center, 550 First Ave., New York, NY 10016. Supported by NMIH grant MH-47277; grant NS-15638 from the National Institute of Neurological Disorders and Stroke; grant RR-00096 from the National Center for Research Resources, NIH; a Senior Investigator Award from the National Alliance for Research on Schizophrenia and Depression to Dr. Brodie; contract DE-AC02-76CH00016 from the U.S. Department of Energy, Office of Health and Environmental Research, to Brookhaven National Laboratory; and a research fellowship grant from the Deutsche Forschungsgemeinschaft to Dr. Schl<148>sser. The authors thank Arlene Hurley and the nursing staff of the New York University-General Clinical Research Center and the Manhattan Psychiatric Center; E. Laska, M. Meissner, T. Cooper, W. Tsui, B. Tewelde, D. Schlyer, J. Fowler, C. Redvanly, C. Shea, D. Alexoff, P. King, D. Warner, N. Pappas, N. Netusil, T. Johnson, and H. Ulyat; and Drs. R. Bilder and A. Wagman for discussions. Dr. Bartlett died during the preparation of this manuscript. Her contribution to the understanding of schizophrenia did not.