To test the hypothesis that alternate-day administration of furosemide will result in a sustained improvement in pulmonary function without causing alterations in electrolyte or mineral homeostasis, we conducted a randomized, double-blind, placebo-controlled study of 11 hospitalized, oxygen-dependent, spontaneously breathing infants with chronic bronchopulmonary dysplasia. Infants were randomly selected to receive either furosemide, 4 mg/kg in two divided doses on alternate days orally, or placebo for 8 days, followed by crossover to the alternate-therapy for an additional 8-day period. The two study periods were separated by a 48-hour washout period. Dynamic compliance, total pulmonary resistance, the concentration of electrolytes in serum, and the concentrations of calcium and creatinine in urine were measured on nontreatment days. Alternate-day furosemide therapy increased dynamic lung compliance by 76 +/- 112% and decreased total pulmonary resistance by 20 +/- 39%, compared with placebo (both variables p = 0.032). Alternate-day furosemide therapy did not result in increased urine output, electrolyte abnormalities, or increased urinary calcium excretion. We conclude that this simplified treatment regimen may be useful in the management of infants with chronic bronchopulmonary dysplasia. The results support our previous speculation that furosemide improves pulmonary function by mechanisms unrelated to its diuretic properties.