Functional magnetic resonance imaging (fMRI) was used to study activation changes in the human primary motor-sensory areas (MAs), supplementary motor areas (SMAs), premotor areas (PMAs) and the superior and inferior parietal areas (SPAs, IPAs) during right hand finger movements as the rate, force and complexity of movement were varied. A preliminary reproducibility study of a single subject doing the same repetitive index finger movements in nine different sessions over a six week period demonstrated highly consistent and highly localized activation in the contralateral MA. ANOVAs demonstrated highly significant main effects of increasing the force and complexity of movement, thereby illustrating the distributed and integrated systemic character of the cortical motor system. Interactions between brain region and the rate and complexity of movements suggested functional specialization of some components of the system. Increasing the rate of movement led to increased activity only in the contralateral MA; increasing complexity led to greater increases in activity in the left and right SPAs and the left IPA than in other areas. Although activation was evident in varying degree throughout the multiple motor areas, only the MAs showed consistent lateralization of activation.