A new rotation therapy technique using slit beams of 10 Mev X-rays (3.3 mm X 50 mm at isocenter FCD 100 cm) was developed. The dose distribution of a 360-degree rotation of the slit beam described above is similar to that of a 137-Cs needle. The axes of a 360-degree rotation of the slit beam were arranged to cover the target volume to produce a dose distribution similar to interstitial irradiation. This technique was named as the slit beam rotation therapy. Twenty patients who had radioresistant tumors or were difficult to control by conventional therapy have been treated with this technique, combined with or without conventional external beam irradiation, since 1982. Eight out of ten extracranial lesions showed good regression and a palliative effect was obtained without severe morbidity. A one year survival rate of 67% in six patients with glioblastoma multiforme was achieved by this method. Although the feasibility study is still in progress, this new treatment technique looks highly promising.