A system in use at Queen Elizabeth College for monitoring the isotopes used by radiation workers and the precautionary medical screening of the workers is described. It consists of a PDP-11 minicomputer and flexible disk storage system. The machine is run under a single-user, real-time operating system and is linked on-line to a teleprinter and a VDU. Data is stored as a series of files, each relating to an individual worker, which can be updated individually from the VDU. The files contain information on the worker's project and medical screening records, and his holdings of isotopes and their use and disposal. A warning is printed automatically if a worker's holding exceeds the allowed maximum. The total quantity of isotopes held and their distribution in an institution such as a university can easily be monitored so that legal limits can be adhered to. The system is inexpensive and can be used by personnel not familiar with computer systems.