The purpose of this set of guidelines is to help the nuclear medicine practitioner perform a good quality lung isotope scan. The indications for the test are summarised. The different radiopharmaceuticals used for the ventilation and the perfusion studies, the technique for their administration, the dosimetry, the acquisition of the images, the processing and the display of the images are discussed in detail. The issue of whether a perfusion-only lung scan is sufficient or whether a full ventilation-perfusion study is necessary is also addressed. The document contains a comprehensive list of references and some web site addresses which may be of further assistance.