Two determinants of adaptation in a mechanoreceptor (Pacinian corpuscle) are described. Both are filters of non-transients. One, a mechanical filter, prevents static components of the mechanical stimulus from reaching the transducer element (nerve ending). This filter is represented by the laminar capsule of the receptor. When the capsule is eliminated by dissection, the generator potential of the nerve ending in response to a sustained stimulus is markedly prolonged. Another filter is represented by an inactivation process of the mechanisms of nerve impulse initiation which prevents a steady outward current from producing repetitive impulses. Both filters cut the duration of the receptor response to a few milliseconds.