The influence of various somatic stimuli on unitary discharges recorded from thalamic nuclei was examined in lightly anesthetized (barbiturate) cat and monkey with lesions of the spinal cord which divided the dorsal funiculus and one ventrolateral column. In the regions explored, the ventrobasal complex and immediately adjacent structures, only a small fraction of the units encountered could be made to alter their activity by nerve volleys or “natural” stimuli. Elements receiving an excitatory projection from the surviving sensory pathways responded to a single volley with a burst of impulses of widely varying initial latency, duration, and recurrence rate. A few estimates of conduction velocity for excitatory primary afferent fibers indicated a large range, 6 to 80 m per second. Each unit of the ventrobasal complex studied was excited by receptors located in a restricted portion of the contralateral body, the effective stimulus being one of the following: hair displacement, light mechanical distortion of the skin, distortion of muscle-fascial relations, joint rotation, pressure, or heat of tissue damaging intensity. Units located in the posterior nuclear group were evoked to discharge by mechanical stimulation of the hair or skin, the most common effective form being a “tap” with a few instances of sound also eliciting a response. The receptive field for posterior group neurons was usually large, often scattered, and frequently bilateral. Penetrations of the intralaminar nuclei and centrum medianum yielded unitary activity excited only by noxious stimuli to bilaterally located regions. A possible artifactitious excitation of neurons by noxious stimuli is discussed. Units are described with “spontaneous activity” in which the only evoked change noted was inhibition as well as a few instances of inhibitory effects on other cells. It was concluded that ventrolateral spinal tracts have projections to thalamic nuclei of a receptor specific place, specific type, and of another type organized in a different manner: each type of projection passing to different nuclear regions and presumably subserving different sensory mechanisms.