Five patients out of a group of ten who had dorsal column electrodes implanted for the relief of chronic pain were examined for the influence of the stimulation on the spontaneous pain and on the thresholds for touch, vibration and cutaneous pain induced by pinching. Stimulation producing paraesthesias resulted in an almost immediate abolishment of spontaneous pain and was accompanied by significant elevations of both tactile and vibratory thresholds. Elevation of thresholds was confined to segments below the site of implantation and occurred bilaterally also when the paraesthesias were restricted to one side. The changes of thresholds generally persisted for some time after the stimulation but these effects were short lasting in comparison with the effect on spontaneous pain. Elevation of sensory thresholds is presumably not due to blocking of the primary neurones but to central inhibitory mechanisms. The thresholds for induced cutaneous pain were not influenced by dorsal column stimulation except for one case in whom an abnormally low threshold within an hyperaestethic area became normalized.