To measure the "line-busy" effect following a flexion reflex in the decerebrate cat a maximal stimulus on the intact portion of the motor nerve (peroneal) was applied at various intervals following a similar stimulus to the central end of a sensory nerve (popliteal or peroneal) and action currents from the end of the motor nerve recorded with a string galvanometer. Continued activity of the motor fibres after the flexion reflex is manifested by a decreased response to the direct stimulus. Such activity, or "line-busy" effect, does not last longer than 30-40[sigma] after the start of the reflex response. The electric responses of a series of flexion reflexes fall progressively to some low value when successive reflexes are elicited by single stimuli at any intervals less than 0.8 seconds. This fall can not, therefore, be due entirely to the "line-busy" effect but suggests an "equilibration" fatigue analogous to that seen in peripheral nerve.