Capillaries in the cerebral cortex of six age groups, ranging between 19 and 94 years (= 34 human brains) were stereologically investigated. Capillary parameters such as diameter, volume fraction, specific surface area, mean intercapillary distances and total length per unit cortex volume in patients older than 75 years were similar to those in young ones, 19 to 44 years old. Aged subjects between 64 and 74 years revealed increased capillary diameter, volume and total length per unit cortex volume, as well as decreased specific surface area. Frequency distributions in the same age indicate a real increase of capillary diameter and volume, as also an increase of these parameters on the level of blood vessels with diamteres greater than 8 micrometer, probably arterioles. The results of this study argue against the wide-spread assumption of a decreased blood supply in the cerebral cortex during old age. On the contrary, the capillary net is able to respond to changed metabolism and blood pressure.