© 2019 Walter de Gruyter GmbH, Berlin/Boston. Halogen radioisotopes have a variety of physical half-lives which are suitable for probing a wide variety of pharmacokinetic processes. Compared with other radiohalogens, relatively little work has been done with radiochlorine. However, high specific activity radioisotopes of chlorine are available from low energy cyclotron production in quantities suitable for positron emission tomography (PET) and fundamental research. In particular, the sole radioisotope of chlorine which may be used for PET imaging, 34m Cl, has achieved a state of development that permits imaging in clinical settings though sparse research effort has been focused on this isotope over the last 40 years. Additionally, the other longer-lived radioisotopes of chlorine will likely continue to show utility for more traditional radiotracer studies and chemistry development.