1. The development of the roentgenographic changes associated with radiostrontium (Sr90)-induced osteogenic sarcomata in the young adult rat is described. Macroscopic and histological features of these neoplasms are also discussed.
2. Intraperitoneal administration of 0.75 microcurie of Sr90 per gram of body weight causes an incidence of osteogenic sarcoma of 65 per cent.
3. The greatest percentage of neoplasms (58.8 per cent) occurred in the spine, followed by 28 per cent in the long bones.
4. The roentgenographic characteristics of Sr90-induced osteogenic sarcomata in the rat and mouse are compared.