<qa>  What is the primary outcome of the study?Pulmonary surfactant is required for normal lung function. Data from a previous study suggest that as many as 75 of chronically ventilated extremely low birthweight premature infants have at least one episode of surfactant dysfunction beyond the first week of life, as measured in vitro, associated with a low surfactant protein B content. Furthermore, episodes of surfactant dysfunction are significantly associated with clinically significant respiratory decompensations. We hypothesize that booster doses of surfactant given during the second and third week of life to extremely low birth weight premature infants requiring persistent intubation and mechanical ventilation will improve their respiratory status during the first 28 days of life. We propose to enroll premature infants 1250 gm birthweight, between days 7 and 10 of life who are intubated, and mechanically ventilated. Infants requiring persistent intubation and mechanical ventilation for respiratory support at 7-10 days of life will receive a total of 3 doses of Infasurf surfactant, 3 days apart, at the standard dose of 3 mlkg. Primary outcome is the change in area under the respiratory severity score curve between days 7 and 28 of life. Total sample size is 88 infants, study duration is 36 months, and recruitment of study patients will occur at The Hospital of the University of Pennsylvania, in Philadelphia PA, Women and Childrens Hospital in Buffalo, St. Louis Childrens Hospital in St. Louis MO, Mercy Childrens Hospital in Kansas City, Oakland Childrens and Alta Bates Medical Center in Berkeley, CA and Long Island Jewish Medical Center, NY. 