The relationship between the interruption of the human pyramidal tract and its attendant clinical manifestations has been a matter of concern to neurologists and neurosurgeons for over a century. We presently report three cases of unilateral pyramidal tract ischemic lesions within the cerebral hemispheres who presented with a contralateral pure spastic hemiplegia syndrome. In none could we find any disturbance in the somato-sensitive evoked potentials of the four limbs. The review of some cases on record since the time of Charcot and Erb has made it clear that the pyramidal syndrome is a valid clinical concept which should be qualified according to the particular animal species one is referring to. In man, it manifests itself by paresis, hyperactive muscular reflexes, spasticity and Babinski sign. Based on this evidence we propose the idea of a «differential control* exerted by the pyramidal tract upon the segmental neuronal pool as its key mode of normal functioning.