I n order to study the reflex effects of activity in different afferent systems one has often in recent work made use of single shock stimulation of a peripheral nerve. I n this way LLOYD (1943, 1946) has carried out a systematic investigation of the coordinated reflex function of different myelinated afferent fibre groups in the hind limb of the cat. Thus it was shown that a single conditioning shock of the large proprioceptive muscle afferents caused a direct facilitation of the synergists and a direct inhibition of the antagonists a t the same joint. A single conditioning shock of the smaller afferent fibres caused an indirect facilitation of the flexors and an indirect inhibition of the extensors.Considering that the sense organs discharge iteratively it is likely that further information about coordinated reflex activity would be gained from an investigation of the central effects produced by tetanic stimulation of the different afferent fibre systems.Several authors have earlier studied how different reflex functions in the spinal cord are affected by prolonged tetanic stiniulation. In these experiments, however, one has generally not taken care to select the effects from the different affgrent fibre systems. Since, in addition the ventral roots have been left intact antidromic effects have complicated the understanding of the results.