Twenty four cases of malignant gliomas, histologically 12 glioblastomas, 10 astrocytoma GIII and 2 astrocytoma GII, were treated by interstitial hyperthermia with Implant Heating System (IHS). IHS has three major parts, generator of high frequency (240KHz), magnetic coil and metal implant manufactured from FePt alloy. Theoretically the brain tumor can be heated by heat conduction through the heated implants. Several implants were placed inside the brain tumor directly by operation, or by CT stereotactic procedure. The patients were divided into two groups according to the tumor location as (A) in cortical or subcortical region (13 cases) and (B) in thalamus or basal ganglia (11 cases). Hyperthermia, 60 minutes each, 2 to 3 times per week, was safely repeated in all the cases. External irradiation was always combined with hyperthermia in most of the cases and with chemotherapy in some of them. Follow-up CTs demonstrate a remarkable response in many cases of B group. In fact ICR, 4PR and 3MR were achieved in this group, resulting in 45.5% of the response. In contrast gliomas in A group showed a less favorable response, resulting in 23.1% of the response (3 PRs in 13 cases). Although the overall response rate was not so high, it seems to be encouraging that gliomas in thalamus and basal ganglia, those which are usually unresectable, showed a good response. More favorable results can be expected by further improvement of the system and related techniques.