The motor conduction velocity of the ulnar nerve of 19 mature dogs anesthetized with pentobarbital was electromyographically determined before and at tissue temperature decrements of 2 degrees (C) during cooling of the forelimb. Precooling (37 C) conduction velocity was 56 +/- 7.6 m/second (mean +/- standard deviation). At a tissue temperature of 20 C, conduction velocity was reduced to 31 +/- 6.3 m/second. Regression analysis indicated that conduction velocity decreased linearly by 1.7 m/second for each degree of decrease in tissue temperature between 37 and 20 C.