We are indebted to Reye Syndrome Task Force Members Lowell T. Harmison, Ph.D., Joel N. Kuritsky, M.D., Ann Rose, Ph.D., and former member Stanley Edlavitch, Ph.D., for their contributions to this study; to Voughn Trader for assistance; to Martha Berlin, Project Manager, for assistance; to Mort Robins, Project Director, and to other study personnel of Westat, Inc., as well as study participants from the Ohio, Oklahoma, and Minnesota State Health Departments and from Cardinal Glennon Memorial Hospital for Children, St. Louis, Children's Hospital, Birmingham, Ala., Children's Hospital of Philadelphia, Children's Hospital of Pittsburgh, Children's Hospital Medical Center, Boston, Children's Hospital National Medical Center, Washington, D.C., Children's Medical Center of Dallas, Denver Children's Hospital, James Whitcomb Riley Hospital for Children, Indianapolis, Ind., Lubbock General Hospital, Medical College of Virginia, Methodist Hospital of Indiana, Primary Children's Medical Center, Salt Lake City, Utah, St. Christopher's Hospital for Children, Philadelphia, St. Louis Children's Hospital, and University Hospital of Upstate Medical Center, Syracuse, N.Y.