[en] A simple and reliable system for the single-breath inhalation and for short-term rebreathing of radioactive gases used in positron emission tomography is described. It comprises a collection- and radioactivity measurement-device, an inhalation bag for single-breath application, a modified anaesthetic system for rebreathing and a patient exhaled gas management system. The system is mainly used with ¹⁵O-labelled gases, but allows also the use of longer lived tracers such as methyl fluoride labelled with ¹⁸F or ¹¹C. (author)