The preliminary results obtained in 19 patients treated with interstitial irradiation for malignant gliomas are reported. Three different groups are included in the study: I Newly diagnosed tumours not suitable for surgery: 13 cases (10 anaplastic astrocytomas (AA) and 3 glioblastomas (GBM), mean volume 46.56 cc, source Ir 192) were implanted permanently (n = 11, mean peripheral dose 93.54 Gy) or temporarily (n = 2, 50 Gy = 0.5 Gy/hr). External beam irradiation was additionally applied in all cases. II Residual or recurrent tumours: 5 patients (2 AA and 3 GBM, mean volume 7.2 cc, source Ir 192) received temporary implants (150 Gy peripheral dose = 1.5 Gy/hr) after surgery and conventional radiotherapy. III Newly diagnosed surgically removable tumours: only one patient with AA (15 cc volume, source Ir 192) received temporary implantation with the same dose regimen used in Group II before surgery and external beam irradiation. A median survival time of 26.75 mos (34.62 mos for AA, with 3 long-term survivors) was observed in the patients of Group I. Three patients of Group II are still alive after 8, 12 and 12 mos after brachytherapy, the other 2 (GBM) survived 7 and 12 mos. The single patient so far included in Group III is still alive after 6 mos. Although the study is still in progress, these preliminary data seem to indicate that interstitial radiotherapy can be effective in prolonging survival of patients with malignant gliomas.