Aerosolized furosemide has been shown to prevent the worsening of different variables in pulmonary function testing, following exercise or bronchial provocation with numerous agents. To investigate if aerosolized furosemide has a bronchodilator effect, we performed two prospective, randomized, placebo-controlled, double-blinded and crossover studies of four aerosol regimens in children with mild chronic asthma. In a pilot study examining three different doses of furosemide in 11 children, the dose of 1.0 mg/kg resulted in a mean maximum increase of 30.0 +/- 6.8% in forced expiratory flow between 25 and 75% vital capacity (FEF25-75), compared with a 3.1 +/- 6.8% increase after aerosolized normal saline. The effect was observed after 10 minutes with a mean percent change of 17.7 +/- 1.7% from baseline, that persisted to 30 minutes (19.3 +/- 3.7%) and was significantly greater than that seen following aerosolized placebo (1.4 +/- 2.9% and 0.7 +/- 3.4%, respectively; P < 0.05). We then compared the effect of furosemide with that of aerosolized albuterol (0.15 mg/kg) in 18 patients. There was no statistically significant difference in the improvement observed in forced expiratory volume in 1 second (FEV1) for albuterol (15.0 +/- 2.7%) compared with furosemide (12.1 +/- 2.9%) or in FEF25-75 (42.9 +/- 9.0% versus 26.3 +/- 6.7%). The addition of albuterol to furosemide resulted in a 17.2 +/- 5.9% increase in FEV1 and a 51.1 +/- 13.9% increase in FEF25-75. Our results indicate that aerosolized furosemide has a bronchodilator effect in children with mild stable asthma.