[en] Under its Statute the International Atomic Energy Agency is empowered to provide for the application of standards of safety for protection against radiation to its own operations and to operations making use of assistance provided by it or with which it is otherwise directly associated. To this end authorities receiving such assistance are required to observe relevant health and safety measures prescribed by the Agency. As a first step, it has been considered an urgent task to provide users of radioisotopes with a manual of practice for the safe handling of these substances. Such a manual is presented here and represents the first of a series of manuals and codes to be issued by the Agency. It has been prepared after careful consideration of existing national and international codes of radiation safety, by a group of international experts and in consultation with other international bodies. At the same time it is recommended that the manual be taken into account as a basic reference document by Member States of the Agency in the preparation of national health and safety documents covering the use of radioisotopes.