The Bereitschaftspotential (BP) recorded from 3 derivations (vertex, left and right precentral areas) in 20 right-handed, normal young subjects was compared in 2 kinds of motor task: a simple movement (task A) and a motor sequence (task B) starting with the simple movement (A). Differences in the onset time and amplitude of the BP were observed: the onset was earlier and the amplitude was larger in the sequential motor task (B) than in the simple one (A). These differences were more important at the vertex (Cz) and in the right precentral area (C4) than in the left contralateral precentral area (C3). These results suggest that the preparatory processes involved in a motor sequence do not exclusively concern the initial movement but also the remainder of the motor task and that the BP is dependent upon the duration or the complexity of the motor task to be executed. The BP seems on temporal grounds to be a global and not a partial expression of a motor task. The changes in the onset time and amplitude of the BP are maximal at the vertex and this could be related to a greater and perhaps earlier activation of SMA in complex sequential motor tasks.