THE TECHNIQUE of decerebration by spatula or suction carries a high mortality in the experimental animal, particularly when an extensive operative preparation precedes it. In a study of the recovery of muscle spindle activity in the chronically decerebellate cat1 we found it necessary to devise some method of decerebration other than surgical section since animals recovering from recent total cerebellectomy tolerated this procedure poorly. Physical agents used effectively in producing lesions in the central nervous system (CNS) of experimental animals include heat lesions with radio frequency current,2 ultrasound,3 and freezing lesions.4-11 Siegfried et al9 and Byck and Dirlik10 produced reversible decerebrate rigidity in cats by cooling the brain stem briefly at intercollicular levels. We have found that this technique can be used to produce enduring decerebrate rigidity in the experimental animal without deterioration or death, thus permitting prolonged periods of physiological investigation. Various