Single-unit recording and intracortical microstimulation techniques have been employed in unanesthetized monkeys in order to ascertain the relative responsiveness of the supplementary motor cortex (MII) and the precentral motor cortex (MI) to a controlled peripheral stimulus. The hindlimb representation was explored to facilitate comparison of MI and MII sensitivity in the same animal. Two main findings have emerged: (i) Many fewer neurons in MII respond to the peripheral stimulus and those that do have much weaker responses than neurons in MI. (ii) The hindlimb representation of MII and the tail representation of MI appear to be considerably further rostral than depicted in the classical maps. The latter finding serves to resolve a discrepancy between the classical physiological and cytoarchitectonic maps for this region of cortex.