Four joggers had early confirmation of clinically suspected stress fractures by radionuclide bone scans. The radioactive bone scan was abnormal as early as six weeks prior to the appearance of conventional roentgenographic changes. The stress fractures involved the bones of the lower extremities and included the femur, tibia, and calcaneus. Radioactive bone scanning also correctly identified stress fractures with bilateral involvement and referred pain. In joggers, when a stress fracture is clinically suspected and the conventional radiographs are negative, a radioactive bone scan is indicated for early confirmation and institution of appropriate treatment. (JAMA 243:1647-1649, 1980)