The detailed variation of the lumen diameter of common carotid arteries throughout the cardiac cycle was noninvasively measured using a pulse-echo ultrasonic technique in a population of 100 free-living, unrelated, human subjects between the ages of 6 and 25 years. The fractional diameter change (mean +/- SEM) during the cardiac cycle in the 50 male subjects (0.122 +/- 0.004) was found to be significantly (P less than 0.001) greater than the corresponding diameter change in the 50 female subjects (0.106 +/- 0.003). The pressure-strain elastic modulus, Ep, for the carotid arteries was also computed for these subjects by dividing the blood pulse pressure measured in the brachial artery by the fractional diameter change of the carotid. The male elastic modulus (67 +/- 3 kPa) was not significantly (P approximately 0.17) different from the female elastic modulus (62 +/- 2 kPa). Subject age and systolic blood pressure were able to explain approximately one-third of the variability in Ep. Reproductibility studies clearly demonstrated that only a small fraction of the remaining variability could be attributed to experimental technique or intrasubject variability. The results suggest that studies can now be safely performed on young human subjects to assess the effects of a variety of developmental, behavioral, and environmental factors on arterial elasticity. Such results could help to establish an important data base on arterial mechanics which might help in evaluating health promotion recommendations to societies.