PURPOSE: To examine the clinical effects of two bronchodilator agents, salbutamol and ipratropium bromide, administered by metered-dose inhaler(MDIS) to preterm infants with respiratory distress syndrome(RDS) during mechanical ventilation. METHODS: This study included 8 ventilated preterm infants with RDS, at a postnatal age of 1 week. The effects of single doses of salbutamol(2puffs, 200mcg) and ipratropium bromide(2 puffs, 36mcg) and placebo(2puffs) given by MDIS were examined in eight ventilated preterm infants. The drugs were each given in an open, random design. Blood gases were measured and ventilatory efficiency index(VEI) and arterial/alveolar oxygen tension ratio(PaO2/PAO2) were calculated five minutes before and 30 minutes after administration. Heart rates and mean arterial blood pressure were noted. RESULTS: The mean PaO2 increased by 5.6mmHg and the mean PaCO2 fell by 2.4mmHg, following salbutamol administration. These results of salbutamol administration were significantly greater than those seen with placebo(P<0.017). Salbutamol caused a significant increase in VEI of 10.4%, significantly greater than the fall of 4.3% seen with placebo. Neither salbutamol nor ipratropium bromide resulted in an increase in PaO2/PAO2 and the effect of both drugs did not differ compared with placebo. Ipratropium bromide did not cause any significant changes in PaO2 and PaCO2. Significant tachycardia was not induced in any of the infants for 1 hour after inhalation of both drugs. CONCLUSION: Salbutamol given by MDIS has useful short-term effects in ventilated preterm infants with RDS.