Detailed evoked potentials (EPs) were studied in 52 patients (28.7 +/- 11.9 years) with Wilson's disease (WD). Various peak latencies, interpeak latencies and amplitudes of somatosensory, auditory brain-stem and visual EPs were significantly abnormal in the group of 28 neurologically symptomatic patients as compared to controls. Interhemisphere latency and amplitude differences tended to be increased without reaching significance, indicating a symmetrical rather than focal subclinical brain involvement. Selected conduction times of at least 1 EP modality were prolonged in all 4 patients with severe, in 16 of 18 with moderate, in 4 of 6 with mild, and in 4 of 24 patients without neurological symptoms. Auditory brain-stem and somatosensory EPs were more frequently prolonged than visual EPs (more abnormalities with check sizes of 13 than 54 min of arc). Cortical somatosensory EPs correlated well (P much less than 0.01) with either Fz or earlobe reference.