Daily weights and mean daily fluid volumes administered to 62 infants with birth weights of less than 2,000 gm, who required respiratory support for respiratory distress syndrome, were reviewed. In 31 infants signs of patent ductus arteriosus developed. In a comparison group of 31 infants, the mean daily fluid volume was 144 ml/kg/24 hours, and the mean body weight was 102% of expected, differing significantly from the 189 nl/kg/24 hours, and 114% of expected weight in those infants who developed PDA. Those infants who developed PDA had not differed significantly from the comparison group in either mean daily fluid volumes or expected weights prior to a period two days before clinical evidence of PDA. Seven infants developed PDA in association with increased fluid administration on more than one occasion during nursery stay. Diuresis after excessive fluid administration was associated with improvement in, or resolution of, signs of PDA in many infants. The results suggest that excessive fluid administration to premature infants with RDS may be one factor associated with the developed of PDA complicating RDS (PDA/RDS).