Short-latency somatosensory evoked potentials by the stimulation of the median nerve at the wrist, were recorded in six patients (four with cerebral tumors and two with post-trauma lesions). The electrodes were placed on the scalp following the 10-20 International System. A reference electrode was placed on earlobe contralateral to the site of the stimulation. Eleven normal subjects were used as control (mean age 64.4 +/- 12.05). We used the Brain-Surveyor-Basis Trade system which allowed us to elaborate the results by coloured mapping through linear interpolation of signal amplitudes. The following parameters were investigated: peak latencies of the N13, N20, P22, N30 waves; amplitudes of the post-rolandic P14-N20, N20-P25, pre-rolandic P22-N30 components and the central conduction time N13-N20 (CCT). The evaluation of latencies was not significant in determining the lesion site. On the contrary, the evaluation of amplitudes revealed expressive asymmetry, though it did not define the nature of alteration (increase or decrease due to lesion), and the correlation between these variations and the site of the lesion. The authors discussed the possibility that amplitude abnormalities in patients with tumors were related either to the tumors and/or drug effects.