This study presents an analysis of the growth dynamics, oncogenic skeletal doses and skeletal locations of radiation-induced osteosarcomas in Beagles at the University of Utah, Division of Radiobiology as of March, 1970. Two hundred and fifty-six well-documented osteosarcomas have been induced in 201 Beagles, each receiving a single intravenous injection of 225Ra (80 tumors). 239 Pu (64 tumors), 228Ra (43 tumors), 228Th (56 tumors), 90Sr (8 tumors) or 224 Ra (5 tumors). Radiographs of each osteosarcoma were taken during the period of the tumor’s growth. The growth dynamics of these osteosarcomas were estimated by measuring the tumor dimension on as many radiographs as possible. It was clearly evident that the tumor volumes were increasing exponentially with time. Exponential growth constants were calculated for 249 tumors; the corresponding volume doubling times ranged from 4.7 to 60.3 days and averaged 12.4 days. Using individual exponential growth constants, a starting time for each tumor was estimated as the time when the extrapolated tumor’s growth curve reached the volume of one cell 10um (um = 10[-4]cm) in diameter. The accumulated average skeletal dose during the time from injection to tumor starting time was calculated for each tumor and called the oncogenic skeletal dose. It was found that the larger the amount of radionuclide injected, the larger the oncogenic skeletal dose. High incidences of radiation-induced osteosarcomas in the Beagles were noted in vertebrae, pelvic bones, humerii, femora and tibiae. Radiation-induced osteosarcomas of the vertebrae and pelvic bones and had much higher incidences than the corresponding incidences of naturally-occurring osteosarcomas in dogs.