TCDO may influence the time of onset, the severity and the healing of radiation-induced ulcers in the rat colon. Endoscopical and histological observations showed that the ulcers were smaller and more superficial after TCDO treatment and that these ulcers did not inevitably cause functional rectal obstruction but healed in a considerable proportion of the treated animals. Contrary to initial expectations, the systemic intravenous or intraperitoneal application appeared superior to the local application of TCDO.