&NA;Matrix support materials for brain surface electrodes used in neuroprosthetic applications were evaluated after chronic subdural implantation over the parietal cortex of the cat. Four types of array fabricated with Silastic, Dacron mesh, or platinum wire annuli were implanted for periods ranging from 5 weeks to 1 year. We evaluated the arrays by access resistance measurements and gross and histological observations of the tissue beneath both nonstimulated and stimulated electrodes. A porous type matrix constructed of Dacron mesh proved to be the superior design because of its minimal compression of the cortical surface, facility of handling during implantation and autopsy, and satisfactory electrical characteristics provided by a good electrode‐brain interface. (Neurosurgery,5: 681‐686, 1979)