The response of the vestibulo-ocular reflex to constant angular acceleration was investigated in healthy subjects using various stimulus amplitudes and stimulus durations. For stimulus amplitudes of 1.06 and 2.13°/s2 the peracceleratory response maximum at 43 s was always followed by a decline in response. This decay was less pronounced for the longer stimulus duration suggesting a nonreturn to the zero baseline. From a comparison with the theoretical model it can be deduced that the gain of the adaptation mechanism is less than unity