Measurements of human femoral arterial wall properties have been obtained transcutaneously in a group of males who were clinically free of arteriosclerosis obliterans. The patients were divided into three groups according to age: under 35, 35-60, and over 60 years. Diameter and changes in diameter were measured using an ultrasonic echo-tracking system. Arterial pulse pressure was determined by the auscultatory method. The results suggest that arteries become stiffer with age. The pressure-strain elastic modulus (Ep) varied from 2.6 ± 0.3 SEM × 106dynes/cm2in the young group to 6.3 ± 1.0 SEM × 106dynes/cm2in the old group. These values are similar to those reported by other investigators using invasive and in vitro technics. Although statistical comparisons indicate a significant difference between groups, there was considerable variation within the groups. Not infrequently, values for Ep obtained from individuals in the oldest group fell well within the range of the values obtained in the young group.