Recent advances in computer-averaged electrophysiological procedures enable the noninvasive recording of activity within somatosensory fiber tracts of higher levels of the CNS in man and experimental animals. In this study, somatosensory-evoked potentials were used to trace the onset of acrylamide-induced distal axonopathy in the primate. Initial dysfunction appeared at the distal extreme of the gracile tract of the dorsal-column system. The peak latency of the SEP component at this site increased by approximately 300 us., preceded any behavioral alterations and appeared coincident with the earliest detectable morphological change in this nucleus.