In this lecture, which celebrates Lauriston S. Taylor, a pioneer in radiation protection and founding president of the NCRP, I review some features of medically administered radioactivity through the past century and attempt to forecast some aspects of its future. I have used as my guide NCRP Report No. 70, Nuclear Medicine--Factors Influencing the Choice and Use of Radionuclides in Diagnosis and Therapy. The following topics are addressed: (1) decision-making considerations in the choice of radiopharmaceutical drug products, (2) factors in choosing an instrument for nuclear medicine procedures, (3) radiation dose, (4) evaluation of radionuclide procedures and their clinical utility, and (5) guidelines for performing nuclear medicine procedures.