Solute and water uptake were studied in isolated perfused rat lungs with airspaces filled with the perfusion fluid. The albumin in this solution was labelled with Evans blue (T-1824), and uptake of fluid from the airspaces was documented by an increase in T-1824 concentration in airway fluid of 6.5 ± 1.6% (n= 5, SEM) at 1 hour and 12.2 ± 0.9% (n= 10) at 2 hours. The only detectable osmotic force that could have contributed to a loss of fluid from the alveolar fluid was a decrease in airspace glucose concentrations, which fell much more rapidly (from 150 mg/dl to 58.7 ± 7.1 mg/dl,n= 10, after 2 hours) than plasma glucose (from 150 mg/dl to 128.9 ± 3.7 mg/dl). Addition of 5 ± 10−5M terbutaline to the perfusate and airspace solutions nearly doubled fluid reabsorption at 1 hour, an effect that was inhibited by propranolol and did not appear to be related to glucose consumption. Exposure to terbutaline for 2 hours increased epithelial permeability to3H-mannitol and22Na+. These observations suggest that active sodium transport and epithelial metabolism or transport of glucose in airway fluid may each play a role in the reabsorption of edema fluid.