Single‐unit activity of the vestibular nerve of the squirrel monkey was recorded with 3MNaCl‐filled ultrapipets. Barbiturate‐anesthetized animals were fixed on a rotating device controlled by a velocity servo. The plane of any semicircular canal could be made to coincide with the plane of rotation. (1) Most fibers are characterized by a regular and high resting discharge (mean, 80 spikes/sec). (2) The response to angular accelerations is consistent with the established morphological polarization of hair cells. The discharge of all fibers innervating a given canal is increased by accelerations, which bend the hairs towards the kinocillium, and decreased by accelerations in the opposite direction. (3) In their dynamic properties, the fibers may be approximated by a first‐order, low‐pass linear system with a time constant of about 5 sec. (4) The dc sensitivity of the fibers averages about 2.3 spikes⋅sec−1/deg⋅sec−2but may vary considerably from one unit to another. [Supported by three NIH grants and an Air Force contract.]