[en] The overall aim of this thesis was to study the development of late radiation induced damage of the rectum and describe the histopathological and morphometric characteristics of the late injury. This required the design of a new, small probe for rectal measurements of cross-sectional area and distension pressure in mice. The impedance planimetric method was developed and validated in vitro and applied in in vivo studies of normal mice. The study of radiation induced damage of the rectum also required a new set-up for selective irradiation of a specific part of the rectum, shielding other organs. Mice were irradiated with varying single doses and followed with impedance planimetric measurements at regular intervals until death of the animals. In order to compare observed changes of the functional properties of the rectum following irradiation, a description of morphometric and morphologic characteristics by a stereolic technique was planned. A simplified stereological method has been applied to this study to describe late morphometric changes in the different intestinal layers after irradiation with varying single doses. (EG)