The clinical records and follow-up data obtained over 13 years on the results of radiotherapy of spontaneous fibrous connective-tissue sarcomas in dogs, cats, and horses were reviewed. The results obtained from the treatment of fibrosarcomas and sarcoids of horses indicated that radiation administered with 60Co is important in the medical and surgical management of these tumors. Fibrous connective-tissue sarcomas in horses were radioresponsive. When radiotherapy was applied postoperatively, the probability of a 2-year cure approached 50% for all prescribed radiation doses of less than 2,000 to greater than 4,000 rads. If radiation doses of 4,500-6,000 rads were used, a 2-year cure rate may approach or exceed 60%.