[long dash]In 15 decerebrate cats the left lumbar sympathetic chain was removed, in 8, before and in 7, immediately after decerebration. Decerebrate rigidity was maintained in the left limbs, and the postural reflexes exhibited by isolated postural muscle preparations were qualitatively unaltered by removal of the appropriate sympathetic nerve chain. It appears, therefore, that the post-ganglionic fibers of the sympathetic nervous system do not constitute the efferent limb of the reflex nervous arc subserving posture in skeletal muscle. The positive changes in posture and postural reflex actions following removal of the left lumbar sympathetic chain in decerebrate cats are briefly: The caudal end of the trunk can be supported at the normal standing height by the right leg but not by the left. A passive flexing force which on the left side is sufficiently great to elicit the lengthening reaction produces on the right side a myotatic contraction due to the stretch reflex. Further increase of this force on the right side elicits the lengthening reaction. The amplitude of the motor response of the crossed extensor reflex (Phillipson''s) is greater on the right side than on the left. The crossed extensor reflex may be produced on the right side by a smaller stimulus (less stretch) than is required for its production on the left side. The knee-jerk is followed by a myotatic contraction which on the left side appears earlier during relaxation and is therefore produced by a smaller stimulus (less stretch) than on the normal side. All changes in posture and postural reflex activity that followed removal of the lumbar sympathetic chain may be explained by the hypothesis that removing sympathetic innervation increased the excitability of the receptor nerve endings in the muscle. This hypothesis may throw light on the function of the fine non-medullated nerve fibers which have been noted to pass to muscle spindles and other proprioceptive end organs.