Flash visual evoked potentials (FVEPs) and brainstem auditory evoked potentials (BAEPs) were performed in 13 children (aged 3-17 years) affected by mucopolysaccharidoses (MPSs). FVEPs and BAEPs were abnormal in 6 and 9 patients, respectively. The presence of these abnormalities in most neurologically normal patients suggests that electrophysiological techniques provide a useful tool for detecting early abnormalities.