Scalp recorded somatosensory evoked potentials (SEPs) elicited by left and right median nerve stimulation were obtained in 21 patients with Huntington's disease (HD), 14 individuals at risk (AR) for HD, and 21 non-patient controls matched for age and sex. Although SEP abnormalities were not uniform in the HD group, no HD patient had SEPs that conformed fully to the normal configuration with respect to peak latencies, presence of all components and spatial distribution. The most common abnormality was non-specific in nature, consisting of amplitude reduction or virtual abscence of components after 100 msec. More specific deviations were noted in the early SEP events. In half of the HD patients, peak P30 seemed to occur at approximately 45 msec poststimulus; this peak could have been taken as the normal P45 had it not reversed in phase between the central and frontal leads. In these cases peak P45 prepared to be missing. Peak N20 latency values were longer in the HD group than in the non-patient controls, whereas the P15 latencies did not differ significantly. The conduction time between P15 and N20 was significantly longer in HD patients than the non-patient controls. SEPs of the majority of the ARs were similar to those of the non-patients controls in terms of overall configuration, although mean amplitudes were generally lower for ARs than non-patient controls and 4 ARs exhibited prolonged P15-N20 latency differences.