Somatosensory evoked potentials (SSEP) to electrical stimulation of the median nerve by using cephalic and noncephalic references were studied to detect the generator sources of short latency evoked potentials in 29 patients with cerebral, brainstem, spinal and peripheral nerve lesions. Patients were divided into six groups according to the localization of their lesions: group 1: cortical and subcortical lesions, group 2: basal ganglion lesions, group 3: pons and mesencephalon lesions, group 4: diffuse cerebral lesions, group 5: cervical cord lesions, group 6: brachial plexus lesions. Potentials were recorded using cephalic and noncephalic references after median nerve stimulation. Evidence obtained from patients suggested the following origins for these short latency SSEPs: P9 may arise in brachial plexus, P11 in dorsal basal ganglions or dorsal column, P13 and P14 in the nucleus cuneatus and lemniscal pathways, N16 in subthalamic structures and most likely mid and lower pons, N18 from the thalamus and thalamocortical tract, and N20 from primary somatosensory cortex.