Intracavitary irradiation of endometrial carcinoma with an afterloading technique, employing Cathetron equipment, was used preoperatively and in patients with inoperable disease as a single therapy or together with external pelvic irradiation. In clinical stages I and II, the survival rates of patients treated preoperatively with afterloading techniques and with the manual Heyman method were quite similar, and the radiation induced complications were less frequent with the afterloading technique. In cases with a large uterine cavity, the one-source tandem method was replaced with a specific two-phase intracavitary irradiation technique. In this method the treatment catheter was positioned against one lateral uterine wall in the first phase, and against the opposite lateral uterine wall in the second phase of irradiation. In experimental studies the shape of the dose distribution curves resembled the uterine shape, and the measured doses were quite similar to those calculated from the radiograms. The treatment results of 32 patients irradiated by this method confirmed its clinical usefulness. Our results show that the afterloading technique is a practical alternative to the manual packing method in the preoperative irradiation of endometrial cancer. With specific instrument modifications the new technique is also useful in cases with a large uterine cavity, whereas the details in the treatment strategies using remote intracavitary irradiation alone or in combination with external radiotherapy need further development.