Sherrington showed that decerebrating an animal to the mid-brain throws extremities and trunk into extensor rigidity which is confined to the muscles which maintain normal posture against the pull of gravity. Such a decerebrated animal, when placed on its feet, stands quite well. This phenomenon Sherrington called reflex standing. Sherrington''s principle regarding decerebrate posture was derived from observations of quadrupeds (cats and dogs), in which all 4 limbs show extensor tonus and are involved in the standing posture. There was some question, however, as to the general applicability of this principle to animals with different normal postures[long dash]man, for instance. In the sloth, which normally hangs rather than stands, normal posture depends on the flexor rather than on the extensor muscles. The decerebrate sloth clearly demonstrates Sherrington''s principle, showing flexor rigidity and reflex hanging, reproducing normal posture. Probable results of decerebration in man are discussed and a case of hemiplegia is cited, showing the physiological characteristics of experimental decerebrate rigidity. A short description of the posture and behavior of the normal sloth precedes the discussion of the experimental findings.