Abstract The essential features of some modern medical cyclotrons, including their installation and starring requirements, are discussed. The more important physical and chemical properties of the radionuclides currently produced by these machines are presented. A cyclotron-produced radionuclide may be selected for clinical or physiological investigations because of a particular physical property, such as short halflife or desirable radiation characteristics, or because no suitable reactor-produced radionuclide is available. Recent medical applications of cyclotron-produced radionuclides are reviewed under four main headings: (i) localisation studies ; (ii) body space estimation; (iii) organ function measurements; and (iv) blood flow measurements. New diagnostic procedures which have been developed by a combination of these radionuclides and the newer techniques and apparatus currently used in nuclear medicine are described. It is concluded that there may be advantages in providing medical cyclotrons in s...