Sixty vestibular nuclei neurons antidromically activated by electrical stimulation of the ventro-posterior thalamus were recorded in two alert squirrel monkeys. The majority of these neurons were monosynaptically activated by vestibular nerve electrical stimulation. Forty-seven neurons responded to animal rotations around the earth vertical axis, sixteen of them also responded to translations in the horizontal plane. The mean sensitivity to 0.5 Hz rotations of 80 deg/s velocity was 0.40±0.31 spikes/s/deg/s. Rotational responses were in phase with stimulus velocity. Sensitivities to 0.5 Hz translations of 0.1 g acceleration varied from 92.2 to 359 spikes/s/g, and response phases varied from 10.1 deg lead to 98 deg lag. The firing behavior in 28 neurons was studied during rotation of the whole animal, of the trunk, voluntary and involuntary rotations of the head. Two classes of vestibulo-thalamic neurons were distinguished. One class of neurons generated signals related to movement of the head that were similar either when the head and trunk move together, or when the head moves on the stationary trunk. A fraction of these neurons fired during involuntary head movements only. A second class of neurons generated signals related to movement of the trunk. They responded when the trunk moved alone or simultaneously with the head, but did not respond to head rotations while the trunk was stationary.