Visual, auditory, and somatosensory evoked responses were recorded from six age groups of Down's syndrome persons and age and sex-matched nonretarded individuals ranging in age from 5 to 62 years and assigned to groups on the basis of observable signs of development and aging. Results indicated that, regardless of stimulus modality, the amplitude of late wave components was dramatically larger for Down's syndrome than for the nonretarded subjects. Where obvious amplitude reduction occurred with maturation and aging among nonretarded subjects, amplitude changes were generally absent among Down's syndrome subjects. The findings for Down's syndrome persons were discussed in terms of deficits in central inhibition and abnormalities in neuronal excitability to different levels of stimulus intensity.