1. From the Pulmonology Division, Department of Pediatrics (P.A.N., D.M.O.), and the Graduate School of Public Health (S.F.K.), University of Pittsburgh, Pittsburgh; and the Pulmonology and Cystic Fibrosis Division, Department of Pediatrics, Case Western Reserve University, Cleveland (C.F.D.). Address reprint requests to Dr. Nixon at the Cystic Fibrosis Center, Children's Hospital of Pittsburgh, 3705 5th Ave., Pittsburgh, PA 15213.