Under standardized conditions two random groups of 28 premature and newborn infants, each mostly suffering from a respiratory distress syndrome, were given infusions of either 60 or 150 ml/kg per day on the first three days of life. On each of the three days an increase of the infusion quantity resulted in a 2--3 times larger urine flow, the osmolal clearance increasing significantly at the same time. This was mainly due to a higher loss of NaCl, whereas there were no significant or only small differences in the excretion of all other electrolytes, acids, and nitrogenous metabolites. There was no clear evidence that a larger fluid intake had an influence on the endogenous creatinine clearance. Considerably negative effects of an increased infusion quantity were not observed in these investigations, yet one should use extreme caution as ductus arteriosus persistens as well as bronchopulmonal dysplasia are attributed to large fluid intakes during the first days of life.