Adaptation, i.e., the decrease with time in sensory units' afferent discharge to a constant stimulus, appears to be a common feature of the receptors belonging to acoustico-lateralis system: However, the mechanisms underlying this process are still a matter of debate. The present experiments demonstrate that sensory adaptation to both mechanical and electrical stimuli can be nearly suppressed after perilymphatic ouabain administration. This clearly indicates that the K+ homeostatic mechanisms [Valli et al., (1990) J. Physiol. (London) 430, 585-594] which control the K+ concentration gradient at both ends of vestibular hair cells play a predominant role in this process. The possible importance of different K+-dependent mechanisms in hair cell adaptation is discussed.