1. From the Division of Epidemiology (E.N., D.K.A.), University of Minnesota, Minneapolis, Minn; Boston Medical Center (E.J.B.), Boston University School of Medicine, Boston, Mass; Rush Medical College (P.R.L.), Chicago, Ill; University of Mississippi Medical Center (T.N.S.), Jackson, Miss; The Jackson Heart Study (H.T.), Jackson Medical Mall, Jackson, Miss; Health Effects Laboratory Division (M.A.), National Institute for Occupational Safety and Health, Morgantown, WV.