Voluntary enhancement and suppression of the vestibulo-ocular reflex (VOR) was investigated in 12 normal subjects aged 23-74. Eye movements were recorded using DC electrooculography in response to two patterns of horizontal rotation: single-frequency sinusoids in the 0.05-0.8 Hz frequency range; and pseudorandom waveforms consisting of a sum of sinusoids in the 0.05-0.35 Hz range. Subjects were able to significantly alter the gain and phase of their VOR responses by fixating imaginary targets in both patterns of stimulation. The amount of VOR modification decreased as the frequency of stimulation increased but was not correlated with age. In the clinical setting, potential voluntary alteration of the VOR must be considered in judging the normality of a subject's responses.