[en] Krypton 81m ventilation and technetium 99m perfusion lung scans in anterior, posterior and oblique views in 86 children (age range 14 days to 15 years) with various paediatric problems were obtained. Four main areas of clinical usefulness were found: (a) Establishing the diagnosis; in a relatively small number of patients the lung scan was essential for establishing the exact diagnosis or directing attention to the abnormal area. (b) Refuting a diagnosis: the two main groups in this category include possible bronchiectasis and inhaled foreign body. (c) Radionuclide studies enable one to assess and follow up the extent of the disease in children with lower respiratory problems; a lung scan may obviate the need for bronchography in bronchiectatics failing to respond to medical treatment and for whom surgery is being considered. Repeat studies are useful in following the natural history or the response to treatment of various lung conditions. (d) Assessing the success of surgical procedures on the heart and on abnormal pulmonary arteries. ⁸¹Krsup(m) ventilation/⁹⁹Tcsup(m) perfusion scanning were particularly useful in small children in whom tests of overall pulmonary function could not be carried out because of lack of co-operation. (author)