Nuclear medicine is the bridge between a particular clinical problem and a relevant test using radionuclides. It began as a minor technical tool used in a few branches of medicine, notably endocrinology and nephrology. However, throughout the world it has become established as a clinical discipline in its own right, with specific training programmes, special skills and a particular approach to patient management. Although the practicing nuclear medicine physician must learn a great deal of basic science and technology, a sound medical training and a clinical approach to the subject remains important. It is for this reason that in the text there has been an attempt to approach the subject from a clinical standpoint, including where necessary relevant physiological material.