The washout of an inhaled water soluble radiotracer from the lungs is a measure of alveolar integrity. Data evaluation of ^99mTc-DTPA studies were previously performed mainly with monoexpoeential fitting with or without background subtraction. The introduction of ^99mTc-pertechnegas for the assessment of alveolar permeability necessitates the investigation of adequate data evaluation schemes for this radiotracer. Methods: We developed a three-compartmental model to describe ^99mTc-pertechnegas kinetics after inhalation. Monoexponential fitting of the first 5 min was investigated as simplification for clinical use. Different background corrections based on blood samples or representative regions of interest were compared. Results: Correction of intra- and extravascular background by subtraction of calibrated curves, which are derived from blood or background areas, resulted in monoexponential washout curves. Clearance rates based on the three- compartmental model were nearly the same as those derived from a monoexponential fit after blood-activity subtraction (r = 0.96). A monoexponential analysis of the first 5 min without any background correction correlates well with the first component of the biexponential analysis (r = 0.97). Conclusion: A dynamic study of more than 45 min allows quantitative determination of the transfer rate of ^99mTc-pertechnegas from the alveoli into the blood using compartmental analysis. A simplified monoexponential analysis of the first 5 min allows assessment of lung clearance without any background correction.