The following investigators, listed in order of the numbers of subjects enrolled, are participating in this study: University of Miami, Miami, Fla: Lawrence Friedman, MD; Lorraine Pall; Donna Maturo; Ann Pasquale. Montefiore Medical Center, The Bronx, NY: Donna Futterman, MD; Dina Monte; Maria Alovera-DeBellis; Neal Hoffman; Stacey Jackson. University of Pennsylvania and the Children's Hospital of Philadelphia: Don Schwarz, MD; Bret Rudy, MD. Children's Hospital of Philadelphia: Mary Tanney, MSN; Andrea Feldman. Children's Hospital of Los Angeles, Los Angeles, Calif: Marvin Belzer, MD; Diane Tucker; Chris Hosmer, MSN; Katie Chung, MSN. Tulane Medical Center, New Orleans, La: Sue Ellen Abdalian, MD; Leslie Green; Chi McKendall; Luann Wenthold. Children's National Medical Center, Washington, DC: Lawrence J. D'Angelo, MD; Connie Trexler; Carleen Townsend-Akpan; Rita Hagler; Julia A. Morrissy, MSW. University of Maryland, Baltimore: Ligia Peralta, MD; Celia Ryder, MSN; Sue Miller; Susan Calianno. Cook County Hospital/University of Chicago, Chicago, Ill: Lisa Henry-Reid, MD; Rosa Camacho. Children's Hospital, Birmingham, Ala: Marsha Sturdevant, MD; Allie Howell; Julie E. Johnson. Children's Diagnostic and Treatment Center, Fort Lauderdale, Fla: Ana Puga, MD; Deanna Cruz; Patricia McLendon. Emory University, Atlanta, Ga: Mary Sawyer, MD; Jennifer Tigner; Ann Simmonds. St Jude Children's Research Hospital, Mitalicis, Tenn: Patricia Flynn, MD; Kim Lett; Jennifer Dewey; Sally Discenza. Mount Sinai Medical Center, New York, NY: Linda Levin, MD; Mary Geiger. University of Medicine and Dentistry of New Jersey, Newark: Paulette Stanford, MD; Felecia Briggs, MS. SUNY Health Science Center at Brooklyn, Brooklyn, NY: Jeffrey Birnbaum, MD; Mohan Ramnarine, MD; Vera Guarino.