Histological evaluations of dog sacral nerves were carried out after stimulation for electromicturition with three types of circumneural electrodes. The use of two types of cuff arrays was associated with a marked buildup of connective tissue around the nerve and filling the lumen of the array. Nerves within the first type of cuff array (having diameters approximately that of the nerve they surrounded) were often extruded from the lumen of the cuff. In some cases, this was accompanied by moderate or marked loss of axons. It is not clear whether this phenomenon was the result of the growth of connective tissue within the cuff or tension on the electrical leads. The damage cannot be attributed to the electrical stimulation because nerves enclosed by nonpulsed electrodes showed similar damage. The second type of cuff array used in the study had an oversize lumen. There was often considerable growth of connective tissue within the cuffs, but minimal or no mechanical deformation of the included nerves and minimal loss of axons. Because of sealable lips, extrusion of the nerve from this electrode was impossible. The nerves and arrays both functioned well, and there was minimal, if any, mechanical distortion of the nerves and minimal neural damage. Nerves within a third type of array ("spinal" array) also showed no or minimal damage. The array was implanted easily, and the delicate, springlike nature of the matrix allowed close apposition to nerves of different diameters while avoiding constriction of the nerve.