Use of high-dose inhaled tobramycin (T) therapy has been advocated for treatment of pulmonary infections in cystic fibrosis(CF). The intent of this study was to examine serum T concentrations following inhaled delivery. Informed consent was obtained from ten CF patients who were prescribed inhaled T dosages>300 mg. All patients were in stable condition as evidenced by physical exam, pulmonary function, and chemistry profile. Whole blood was collected prior to ultrasonic T aerosolization, 0.5, 1, 1.5, 2, 3, and 6 hours following T delivery for analyses of T content using a fluorescent immunoassay technique. Serum T pharmacokinetics (AUC; Tmax; Cmax) were estimated using a one-compartment with equal first-order input and first-order output model (PCNONLIN™). Subjects (6 Male/4 Female) ranged in age from 10 to 43 years and inhaled T dosages ranged from 400 to 600 mg. Serum T concentrations ranged from undetectable to >20 μg/mL in one subject. Subject's AUC, Tmax, and Cmax for the pharmacokinetic model ranged from 1.6 to 60.5 mg L/hr, 0.7 to 1.8 hr, and 0.2 to 11.1 μg/mL, respectively. Under the experimental conditions of this study, unexpected intersubject variability was observed. Albeit, nine of ten subjects had peak T concentrations<1 μg/mL; significant absorption was observed in one subject. Further investigations may be justified to identify factors attributable to significant T absorption following inhalation.