Positron emission tomog. (PET) has become a powerful tool for non-invasive investigations of basic biol. and physiol. processes in vivo, for example: blood flow, transport and metabolism of natural substrates and localization and characterization of receptor systems. The aim of the synthesis of short-lived radiotracers is to develop the PET probes. Cyclotron-produced 11C(t1/2:20min), 13N(t1/2:10min), 15O(t1/2:2min) and 18F(t1/2:110 min) are gaining ever increasing attention and being actively utilized in clin. research and application, because they could be incorporated into naturally occurring biomols. or drugs of various class without alteration of the compounds' defined functions in living systems. During recent years many 11C and 18F-labeled ligands have been synthesized for a no. of receptor systems such as opiate, dopamine, serotonin, benzodiazepine, histamine, nicotine and muscarine. Ohmefentanyl, a new, highly potent and selective agonist for opiate m-receptor found in the authors' laboratory, was labeled with carbon-11 in CEA, France.

Key words: DIAGNOSTICUM