The amount of collagen and elastin in normal canine arteries was determined biochemically in nine different sites. The total collagen and elastin ranges from 58 to 75% of the weight of the dry defatted artery. Reasons are adduced to propose that the expression of results as the ratio of collagen to elastin (C/E) is a useful index of the relative distensibility for the maintenance tension of arterial wall. Two arteries, carotid and renal, which are pathways to blood pressure sensors, have a statistically significantly higher C/E than the femoral and mesenteric arteries, which are pathways to regulated beds. The highest C/E was found in the coronary artery. Results are interpreted in relation to the function of the vascular beds to which the representative arterial specimens belong.