It is known, that brain gliomas may progressing and become more malignant as comparison with in an initial stage. At the same time not take into account the decisive role of tumor - association inflammation (TAI), which accompanies gliomas growth and progression. It is quite possible, that exactly TAI promoting malignancy of tumor process. With the purpose of confirm or disprove this assumption, the sophisticated experiments was carry out with implantation glioma 101.8 cells into embryonic rat brains, in which inflammation is absence, and with combined cultivation in vitro rat normal embryonic cells with high malignant glioma 101.8 cells. It was reveal cytolysis of malignant glioma 101.8 cells to be in touch with embryonic cells in experiments vivo and in vitro. While after combined inoculations into adult brains death of rats was observed as a result of invasive tumor growth. Consequently, one of the main reasons of glioma malignancy is tumor-association inflammation, in the absence thereof high malignant glioma cells losing its malignancy.