1. From the General Internal Medicine Section (111A1), Medical Service, Department of Veterans Affairs Medical Center (J.A.S., W.S.B.), and the Division of Clinical Epidemiology, Department of Epidemiology and Biostatistics, University of California (J.A.S., J.F., W.S.B.), San Francisco, Calif; and the Clinical Biochemistry Branch, Division of Environmental Health Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, Ga (J.T.B.).