Abstract The development of radiotracers with defined affinities for specific receptor systems is a potentially useful approach to the design of radiopharmaceuticals for nuclear medicine. Radiolabelled ligands, such as hormones and neurotransmitters, are being synthesized and evaluated as diagnostic tools for diseases which can be characterized either by changes in receptor concentration or by novel receptor expression. Since the utility of a radiopharmaceutical is dependent upon the achievement of adequate ratios of target to nontarget accumulation of radioactivity, design of radiotracers via the receptor approach attempts to exploit those systems in which receptor is present in significantly higher concentration at potential target sites such as tumors. Receptor-mediated radiotracers are also currently being used in animal models to investigate the normal tissue distribution of drug and hormone receptors and the in-vivo pharmacokinetics of receptor binding. The successful development of receptor-avid radiopharmaceuticals will depend on the ability to synthesize ligands of high specific radioactivity which retain the high affinity and binding specificity for the receptor after radiolabelling.