Twenty-eight patients with early-stage carcinoma of the uterine cervix were treated using one standard Manchester radium application and one afterloading Selectron application. In each case, radiographs were analysed to determine differences in geometry of applicators relative to each other, or to the bony pelvis. During the Selectron treatment the applicators lay significantly more anterior in the pelvis, with a reduced angulation between the axes of the uterus and the vagina. The separation between the ovoids was increased. An identical analysis of 25 patients who had received two radium applications showed that the uterine tube lay significantly more anterior in the pelvis during the second application. Reasons for these differences and their possible clinical importance in terms of increased dose rate to critical tissue are discussed.