This International Standard specifies the classification, general design requirements, performance characteristics and test procedures for in vivo counting systems for detecting trace amounts of radionuclides in the bodies of persons working in nuclear power plants, laboratories and facilities handling radionuclides, and inhabitants living on territory which may be contaminated by either naturally occurring or artificial radionuclides. The purpose is to determine the dose equivalent to organs and the effective dose of internal radiation for the whole body. This standard is applicable both to equipment with spectroscopic capabilities and instruments for rapid screening for gross internal contamination only. This standard is applicable to instruments for the monitoring of certain critical organs (for example, lungs, thyroid gland, etc.) as well as instruments for monitoring the whole body. The standard applies to equipment for the measurement of the activity of gamma-emitting radionuclides in humans in order to determine the committed dose equivalent due to internal contamination in accordance with the recommendations of the ICRP 60 and ICRP 61. The requirements of the standard are applicable to the installed apparatus, to vehiclemounted equipment and to portable instruments. However, Annex B defines the additional mechanical and environmental performance requirements and the additional testing required for transportable and portable assemblies. The general and radiological requirements of all types of in vivo counters are included in this standard. Depending on the type of instrument and the organ to be checked, measurement geometry may require the subject of the monitoring procedure to stand, sit, or lie. The detection assembly includes one or more radiation detector. Normally, these are shielded-scintillation or semi-conductor detectors. Where identification of the location of contamination is required, the detectors may be collimated. The measurement assembly includes functional units for the processing of signals from the detection assembly as well as units for the display of the measured activity. For the measurement of body mass a built-in weighing machine may be used.