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Different tracers have been proposed in nuclear medicine to visualize neuroendocrine tumours; the majority are based on specific uptake mechanisms while some are aspecific. Among the most important gamma-emitting tracers, radiolabelled metaiodobenzylguanidine (123I or 131I-MIBG) and 111In-pentetreotide should be mentioned. In particular, good results can be obtained with 111In-pentetreotide scanning, which visualizes more than 70% of all neuroendocrine tumours and in some indications, as in gastro-entero-pancreatic (GEP) tumours, has a diagnostic sensitivity superior to that of conventional radiological imaging. Radiolabelled monoclonal antibodies have at present only a storical value, while a series of new peptides represent interesting subjects in areas currently being regarded.