A study of effect of local hypothermia upon the paravertebral muscles which also become sensitized during spinal cord cooling was performed using cats. With a cuff, a cooler, to which was attached tubes connected to a refrigerator, the experimental technique was deviced to cool the paravertebral muscles locally at cervical and lumbar level. Cold, liquid saline at a temperature of 2.8+/-0.6 degrees C was circulated in closed system through the tube into the cuff which was snugly rested on the surface of paravertebral muscles as a heat exchanger. The temperature was measured at intervals of ten minutes with thermocouples before and during cooling for thirty minutes. In the muscle surface underneath the cuff, the mean precooling temperature of 30.1 degrees C in the normal muscle was lowered to 15.4 degrees C at the end of the first 10 minutes of cooling. After this initial rapid drop in temperature, there was a further gradual decrease of temperature to 13.6 degrees C at the end of 20 minutes of cooling. In the muscle 1cm beneath the cuff, the mean precooling temperature of 31.4 degrees C in the normal muscle was lowered to 17.3 degrees C at the end of first 10 minutes of cooling. After this initial rapid drop in temperature, there was a further gradual decrease of temperature to 16.2 degrees C at the end of 20 minutes of cooling. For comparison, the temperature in the clipped muscle and nonclipped muscle were also measured. The temperature in the clipped muscle surface was lower than that of non-clipped. Topical ice application resulted in rapid drop of temperature from 31.2 degrees C to 13.9 degrees C in skin, 32.3 degrees C to 13.1 degrees C in subcutaneous layer and 32.5 degrees C to 13.9 degrees C in muscle, simultaneously. Another aspect of this experiment was an evaluation of the protective effect of local hypothermia with respect to muscle injury associated with clipping, of muscles. The injured(clipped) muscles with or without local hypothermia was biopsied and stained with Hematoxylin Eosin and Hematoxylin Basic Funchsin Picric acid and sectioned specimens were observed under the light microscope. The clipped muscle examined thirty minutes after release of clipping showed 20~30% of red stain in HBFP stain. The normal muscle showed less than 5% of red stain in the field. In intermittent hypothermia, 2 minute cooling group showed 20% of red stain in the field. The clipped muscle with local hypothermia showed less red stain than that of non-hypothermia. The results of this study confirmed the belief that the cold liquid and ice of physiologic saline can be used in clinical neurosurgery for extravascular local cooling of scalp and paravertebral muscles and for irrigating or perfusing operative field.