Krypton-81m, an inert, radioactive gas with a physical half-life of 13 seconds was used to evaluate regional lung ventilation in 25 pediatric patients. The results suggest that Kr-81m has several advantages over previous methods employing xenon-133. These include: more favorable physical characteristics for imaging with present scintillation cameras; ease of performance of the examinations; improved resolution and multiple views with better detection and localization of abnormalities; and a much lower dose to the patient.