Somatosensory evoked potentials were recorded at Erb's point, over the cervical spine (C7) and over the cortex: parietal and frontal electrodes were contralateral and ipsilateral to the stimulus which was applied on the median nerve at the wrist. The stimulation was performed on 2 control groups, the first consisting of 10 subjects (average age: 33.6 years), the second of 16 subjects (average age: 66.2 years) and on 6 patients presenting unilateral thalamic lesions. These lesions were circumscribed, ischaemic or haemorrhagic and were visualized by a scanner. In 5 of our patients, a diffusion of the P14 wave with normal latency and a delay in the N20 cortical wave was obtained at the parietal electrode contralateral to the stimulus and homolateral to the lesion. Normal latencies were observed for the diffusion of the N18 wave recorded at the frontal electrode contralateral to the stimulus. In the 6th patient, the evoked potentials were normal. The results of the somatosensory evoked potentials observed in our patients are discussed in the context of the anatomical lesions.