Single unit activity of second-order vestibular neurons was recorded in alert guinea pigs. Here, we compared the spike discharge regularity (measured by calculating the coefficient of variation (CV)) of neurons from control animals with those from animals labyrinthectomized 1 week before. The mean CV (+/-SD) were the same in both groups (0.72+/-0.43 vs. 0.70+/-0.39). Furthermore, in both groups, the CV was related to the resting rate (RR) according to the same law (CV = 4/square root of RR). Because the discharge of a neuron is more regular when it is due to a pacemaker activity than when it is due to the synaptic drive, we conclude that restoration in the firing rate after labyrinthectomy is due to increase in the synaptic drive rather than to increase in the (intrinsic) pacemaker activity.