11 patients with recurrent brain tumours underwent intraoperative radiotherapy (IORT) at a dosage of 15-25 Gy of fast electrons (17-20 MEV). IORT allows a higher dose of irradiation to be delivered to a well-defined target than is possible with external radiation, in anticipation of favourable results. However, tumour growth was not influenced in 7 out of the 11 patients and these patients died between 2 and 10 months following IORT. The remaining four patients are living still up to 15 months postoperatively. Due to the inhomogeneity of our patients no definitive conclusions can be drawn. However, well-defined tumours which can be radically excised are definitely more suitable for IORT than large, infiltrating tumours.