High iron-containing silicate glasses were prepared using a conventional melting and quenching process, and ferrimagnetic crystallites were precipitated via a nucleation and crystal growth mechanism. This study attempted to use these ferrite-containing glass-ceramics as thermoseeds for a hyperthermic cancer treatment under an alternating magnetic field. KB and L929 cells were used in the cell lysis experiments, as carcinoma and normal cells, respectively. These cells were mixed with an agar medium and stained prior to the annihilation test. After exposing the cells to the alternative magnetic field for 9 min, the number of carcinoma cells in the vicinity of the ferromagnetic specimen decreased with increasing time and almost all cancer cells were dead after 9 min while they were still alive in a region of 5 cm away from the specimen. When Sprague-Dawley rats imbedded the samples were exposed to a magnetic field, tumor cells disappeared after only 4 treatments of 15 min each. This amazing reduction in the tumor was not observed in any rats without the imbedded sample. It is expected that the prepared ferrite-containing glass-ceramics will be helpful in hyperthermic cancer treatment. Long-term research is needed to confirm this result. (C) 2003 Kluwer Academic Publishers.