To evaluate the relationship between spontancous diuresis and improvement of pulmonary function in respiratory distress syndrome, 15 premature neonates requiring mechanical ventilation for RDS, who admitted in NICU of Wonkwang University Hospital from January 1990 to June 1992, were studied. The results were as follows (results are mean+/-SEM) 1) Mean birth weight of study infants was 1.82+/-0.08Kg, and mean gestational age was 32.80+/-0.54 weeks. 2) The onset of diuresis occured at a mean age of 29.1+/-2.48 hours with maximum diuresis at a mean age of 41.9+/-1.8 hours 3) Mean urine output increased from 2.25+/-0.43ml/Kg/hr at the stage of pre 12 hours-onset of diuresis (p<0.001), then decreased 3.5+/-0.2ml/Kg/hr at the stage of after maximum diuresis (p<0.05). 4) After maximum diuresis, inspired oxygen gradient, peak inflating pressure, peak end expiratory pressure, mean airway pressure, and respiratory rate were decreased significantly (p<0.05), and alveolar-arterial oxygen gradient was decreased more significantly (p<0,01). So, We conclude that the pulmonary function was rapidly improving after maximum diuresis and these changes reflect the general principle used in ventilatory management of infants with RDS.