Flies rely on a powerful gaze stabilization reex to facilitate visual control and guidance of ight. We performed behavioral experiments and systems identification to study the contribution of two major sensory systems to gaze stabilization: the mechanosensory halteres, and the compound eyes. We measured the frequency response of compensatory head roll induced by forced thorax movements with and without halteres. Based on a simplified, linear architecture, we derived transfer functions for the two sensory pathways and the neck motor system that actuates changes of head position. The resulting bandwidths and response delays were consistent with data from the literature. © 2011 IFAC.