The thickness of the media of the aorta and the carotid, iliac, and renal arteries was measured in hibernating and nonhibernating marmots. A positive correlation was found between body weight and the thickness of the media of carotid and iliac arteries. The relation noted apparently was not due to the mean arterial pressure prior to and during hibernation, since there was no difference in the thickness of the media between nonhibernating and hibernating females. The difference due to gender could be accounted for by the greater average body weight of males. The media of the renal arteries demonstrated no relation between their thickness and body weight.