Experiments were carried out in 37 animals (33 test animals and 4 controls). Hypokinesia was produced by keeping the animals in small cages. After 1, 2, 3, 4, 5, 6, 8, 12, 16 weeks of restricted mobility the animals were killed. The brain blood vessels were injected with dye-stuffs and examined in cleared sections. In 9 animals (2 controls and 7 test animals) the brain blood vessels were studied histochemically. Hypokinesia was stated to change significantly the angio-architectonics of the telencephalon. During first three weeks of restricted mobility, the blood vessels change but a little. By that time, together with unchanged arteries and veins, narrow arteries and a great number of dilated veins are encountered. The density of the blood vessel network is altered. Later on, after 4 weeks, more profound changes in the blood vessels occur: they become tortuous, deformed with disturbance of their usual orientation of course. These changes are specific for all the parts of the telencephalon. They increase with the time of hypokinesia.