Studying the proliferative activity of 60 astrocytic gliomas in the cerebral hemispheres by immunohistochemical detection of proliferative nuclear antigen in their nuclei has revealed that the expression of this cancer proliferative marker statistically significantly differs in the labelling index of proliferative nuclear antigen in benign and anaplastic astrocytomas (5.2 and 34.7%, respectively). Analyzing the relationships between the proliferative activity of astrocytic gliomas to their histostructural features has ascertained that there are higher proliferative nuclear antigen labelling induces in the astrocytic gliomas along with mitotic figures, proliferation of the vascular endothelium, vesicle-shaped nuclear, and multinuclear cells, the two latter signs are of greater importance as they are much more frequently encountered. The above-mentioned histological signs may be regarded as criteria for diagnosis of malignant transformation of astrocytomas.