This article reports on the selectivity experimentally obtained with a hand-made 24-fold 2D array with electrodes spaced at 120 μm in the rat peroneal nerve and extensor digitorum longum muscle. We call the device 2D, as all the electrode tips lie in the same plane. The device itself is a 3D multiple needle array. The design and construction of a 128-fold 3D array in silicon- and glass technology is briefly described, as well as the fabrication of a 2D 128-fold array in silicon- and LIGA technology. Special attention is given to efficiency; i.e., the ratio of the number of successful electrodes contacting a single motor fiber to the total number of electrodes in the device. We also discuss whether microfabrication technology will allow a further increase in the number of electrode sites, or if an alternative way of interfacing, namely employing cell cultures on electrode substrates, will lead to higher efficiencies.