Cortical potentials related to freely-executed voluntary wrist flexion (MRPs) were studied in 35 subjects aged 23-80 years. The characteristics of the MPRs in aged subjects were determined in comparison data from 14 young subjects aged 23-40 years. The analysis concerned 3 components of the MRPs: the slow negative shifts (NS1 and NS2) before the movement onset and the motor potential (MP). In the aged subject, the latencies measured at Cz show a significant lengthening of the NS1 and of the duration of NS2 (NS' of Shibasaki et al, 1980). The mean amplitude of the NS1 peak at Cz is decreased, and those of N1 (the negative peak before the movement) and MP are not significantly different from those of the young subjects. The NS2 component in the aged subject (between NS1 and N1) is thus increased. In contrast to the young subjects, who present a predominance of N1 and MP amplitudes of the contralateral motor cortex over the ipsilateral cortex, the aged subjects lose lateralization of these components. Recording of MRPs with subdural electrodes (Neshige et al, 1988) shows taht NS1 results from the activity of the supplementary motor area and from the ipsi-contralateral primary motor cortex. The increase in NS2 might be interpreted as an expression of activity coming from other structures to compensate for the reduction in NS1 in the aged subject and to maintain the level of the motor potential MP.