The cerebral arterial smooth myocytes of dogs with experimental hypertension (n=12), its correction (n=10), and of intact dogs (n=8) were studied. The structure of myocyte population changed under conditions of vascular wall hyperfunction: the size of the cytoplasm and nuclei, DNA content in the nuclei, mitotic activity, and percentage of binuclear forms increased. Thickening of the tunica media in intraorgan arteries was caused by such cytological mechanisms as leiomyocyte hyperplasia and hypertrophy. The cells shrank after elimination of hypertension, while vascular polyploidy persisted.