We studied 170 premature infants with birth weights between 751 and 2000 g in a randomized sequential trial comparing "high" and "low" volumes of fluid intake. Beginning on the third day of life, the low-volume group received only enough water to meet average estimated requirements, and the high-volume group received an excess of at least 20 ml per kilogram of body weight per day (mean excess, 47 ml per kilogram per day). Sequential analysis showed that the risk of patent ductus arteriosus with congestive heart failure was greater in infants receiving the high-volume regimen. Thirty-five of 85 infants in the high-volume group acquired murmurs consistent with patent ductus arteriosus, and 11 of these 35 had congestive heart failure. Only nine of 85 infants in the low-volume group had murmurs consistent with patent ductus arteriosus, and two of these nine had congestive heart failure. More cases of necrotizing enterocolitis also occurred in the high-volume group. We conclude that limitation of fluid intake to amounts estimated to meet requirements for excretion, insensible loss, and growth can reduce the risks of patent ductus arteriosus and congestive heart failure in premature infants.