Nuclear medicine in otolaryngology. Nuclear medicine has a distinct role to play in otolaryngological practice. Accurate diagnosis of endocrine conditions is now possible using precise in-vitro hormone measurement. Specific clinical questions can be answered using in-vivo investigations. 99mTcO-4/123I scintigraphy is used to evaluate thyrotoxicosis and solitary thyroid nodules. 99mTc/201T1 subtraction scanning is of value in the preoperative localization of parathyroid adenomas and 99mTcO-4 is particularly useful in assessing salivary and lachrymal gland function and drainage. 99mTc-MDP bone scanning is useful in the evaluation of osteomyelitis, temporomandibular joint dysfunction, bone graft viability and some facial fractures. The role of radioisotopes in the management of differentiated and medullary carcinoma of the thyroid is now well established. Although there are many other agents available to image head and neck cancer, few can actually achieve the required diagnostic sensitivity and specificity. The introduction of monoclonal antibodies into routine imaging has been hampered by distinct practical problems and the search is now on for more sensitive non-specific diagnostic agents. It is now possible to evaluate new 99mTc labelled tumour-imaging agents using animal tumour model systems and the use of radioactivity in all aspects of otolaryngological research adds an extra quantitive dimension. Together with SPECT, and the introduction of positron emission tomography (PET) to image the physiology of normal tissues and tumours, the use of radionuclide investigations can lead only to an increase in ENT diagnostic sensitivity and specificity and, subsequently, to an overall improvement in the way we diagnose, stage and treat head and neck cancer. 