Abstract The authors describe the design and development of systems for direct in vivo measurement of dose within the living subject. They have used the method since 1957 for therapy, diagnosis, nuclear medicine, and radio-biology. The systems include home-grown and commercial luminescent solid state dosimeters of various types and geometries, read-out instrumentation, and a methodology for implantation and removal of dosimeters in virtually every body organ and tissue in living patients and animals.