Presented at the annual meeting of the Research Society for Alcoholism, Santa Barbara, Calif., June 26–July 1, 1999. Received Feb. 8, 2000; revisions received June 16 and Sept. 26, 2000; accepted Oct. 23, 2000. From the Departments of Psychiatry, Medical and Molecular Genetics, and Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis; the Department of Psychiatry, University of Iowa, Iowa City; the Department of Psychiatry, Washington University at St. Louis; and the Department of Psychiatry, University of California, San Diego. Address reprint requests to Dr. Nurnberger, Department of Psychiatry, Indiana University Medical Center, 791 Union Dr., Indianapolis, IN 46202-4887; email@example.com (e-mail). The authors thank Kathleen Bucholz, Ph.D., for comments on the manuscript and Henri Begleiter, M.D., Ingrid Schmidt, and Ting Kai Li, M.D., for administrative support for the National Institute on Alcohol Abuse and Alcoholism Collaborative Study on the Genetics of Alcoholism. The Collaborative Study on the Genetics of Alcoholism (H. Begleiter, State University of New York, Health Sciences Center at Brooklyn [SUNY HSCB] principal investigator, T. Reich, Washington University at St. Louis, co-principal investigator) is supported by grant AA-08403 from the National Institute on Alcohol Abuse and Alcoholism and includes nine sites, each with its own principal and co-principal investigators: Indiana University (T.-K. Li, J. Nurnberger, Jr., P. M. Conneally, H. Edenberg); University of Iowa (R. Crowe, S. Kuperman); University of California at San Diego (M. Schuckit); University of Connecticut (V. Hesselbrock); SUNY HSCB (B. Porjesz, H. Begleiter); Washington University at St. Louis (T. Reich, C. R. Cloninger, J. Rice, A. Goate); Howard University (R. Taylor); Rutgers University (J. Tischfield); and the Southwest Foundation (L. Almasy). Also supported by grant AA-00285 from the National Institute on Alcohol Abuse and Alcoholism (T. Foroud, principal investigator).