Spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHRSP) were treated with a combination of a beta 1-blocker (Metoprolol) and a calcium antagonist (Felodipine) from 1 to 4 or from 4 to 6 months of age. Cross sections of plastic embedded basal cerebral arteries were measured with a digitizer. The ratio between media thickness and luminal radius (m/r ratio) could then be calculated for a standardized condition assuming a smooth, circular internal elastic membrane. The treatment caused a significant decrease of the m/r ratio in various basal cerebral arteries of young and adult SHR and SHRSP, i.e. the therapy may prevent as well as reverse hypertensive structural changes. Unilateral superior cervical ganglionectomy or preganglionic denervation did not affect the structure of basal cerebral arteries in young SHRSP or normotensive controls. A slight decrease of m/r ratio was indicated in the smallest pial arteries on the sympathectomized side, but the results did not allow any conclusion as to differences in effect between preganglionic denervation and ganglionectomy.