To determine the relationship between improvement in pulmonary function and diuresis in respiratory distress syndrome, ten consecutive premature infants requiring mechanical ventilation for severe RDS were studied. Every infant had a diuresis (output/intake greater than 80%), which began at 26 to 34 hours of life and which lasted for an additional 64-72 hours. The diuresis preceded significant improvement in AaDo2 and ventilator settings (IMV, PIP, PEEP) by 52 hours. There was a significant decrease in body weight among all study infants during the first four days of life despite an increase in fluid intake. This study suggests a relationship in RDS between improvement in oxygenation and removal of interstitial lung edema.