 In NICHD Neonatal Research Network NRN centers in 2002, phototherapy was administered to 94 percent of the extremely low birth weight ELBW infants who survive more than 12 hours. Yet, it is unclear what level of bilirubin in the blood is harmful for these very tiny infants -- no data existed from large or recent clinical trials to define the risks, benefits, and appropriate indications for phototherapy in these infants. The largest and most recent trial was the NICHD Collaborative Phototherapy Trial which involved infants treated in 1974-1976 and included only 77 ELBW infants. Data from this study and others suggested that phototherapy could have important hazards as well as benefits for ELBW infants. 