A pioneer in pediatric medicine education and research, THE CHILDREN'S HOSPITAL OF PHILADELPHIA has fostered clinical innovations and scientific breakthroughs that have advanced pediatric health care worldwide. Children's Hospital was ranked as the best pediatric hospital in the nation in 2003 by U.S. News & World Report and Child magazines. All three editors are on staff at The Children's Hospital of Philadelphia: JULIAN LEWIS ALLEN, M.D., is the Chief of the Division of Pulmonary Medicine and Cystic Fibrosis Center and the Robert Girard Morse Endowed Chair in Pulmonary Medicine; TYRA BRYANT-STEPHENS, M.D., is the Medical Director for the Community Asthma Prevention Program; and NICHOLAS A. PAWLOWSKI, M.D., is the Allergy Section Chief of the Division of Allergy and Immunology. SHEILA BUFF and MARTHA M. JABLOW are professional writers.