Mechanically vibrating a skeletal muscle elicits reflex activation of that muscle, a phenomenon which is known as the tonic vibration reflex. We explored in eight individuals how vibration of their right biceps brachii or triceps brachii muscle influenced their ability to point with their left arm to visual targets and to set that arm to particular apparent positions. The position sense of the pointing arm was affected systematically by contralateral vibration with the influence being considerably greater when the biceps brachii rather than the triceps brachii of the contralateral arm was stimulated. This asymmetric effect was related to the different densities of muscle spindle innervation of the biceps brachii and triceps brachii muscles and to their patterns of reflex organization within the spinal cord. The altered position sense of the pointing arm led to errors both for pointing movements with the arm to visual targets and for positioning movements of the arm into specified spatial configurations.