The galvanic vestibular stimulus (GVS). created by applying a small current to electrodes placed behind the ears, elicits a postural sway response in humans during stance. While this technique has been used both to study the role of vestibular sensation in the control of posture and as a diagnostic tea of vestibular function, there are still gaps in the understanding of this response. The goal of this study was to investigate the effects of the stimulus frequency, stimulus intensity, and initial conditions on the subsequent postural response. Ten healthy adults, aged 22 to 31 years, were studied in two protocols. In the first experiment the subjects experienced continuous sinusoidal GVS at multiple frequencies (0.1. Q25.0.45. and 1.1Hz) and amplitudes (0.05, 0.1, 0.25, 0.5, 1.0 mA). In tire second experiment a 0.5 mA pulse was applied for five seconds. In both experiments, the displacements of the both segments and of the center of pressure (COP) were monitored before, during, and after stimulation. The results of the first study demonstrated that die magnitude of sway and its phase relationship with the stimulus varied with stimulus frequency and stimulus amplitude. The effect of decreasing the frequency or increasing the amplitude of the stimulus was to increase the magnitude 3nd decrease the phase lag of the response. In the second study, the postural initial conditions wierefotmd to have a significant effect on the magnitude of the response. An initial position in the direction of the anticipated GVS response decreased the magnitude of the response, whereas, an initial position centered over the base of support or opposite the direction of the anticipated GVS response did not affect the magnitude of the response. The effect of increasing the initial velocity was to increase the magnitude of the response, regardless of the direction of the initial velocity . These studies suggest that stimulus frequency, stimulus amplitude, and postural initial conditions are all important factors in detemuning the postural response to GVS. The appropriate choice of these parameters leads to larger and more robust responses. These findings have important implications both for fixture studies of the role of vestibular sensation in the control of posture and in the development of new' galvanic tests of v estibular function.