Objective: Arterial distensibility (DC) and compliance (CC) are vessel wall properties of large arteries that can be measured non-invasively with a custom made vessel wall movement detector system (VWMDS). This study investigated the reproducibility of this device in 10 volunteers. Methods: To investigate intraobserver intrasession and intraobserver intersession variability, arterial diameter (D) and relative change in diameter during the heart cycle (ΔD/D) were measured in the elastic common carotid artery, and in the muscular femoral and brachial arteries. Interobserver intrasession variability was examined in common carotid artery by two observers, while interobserver variability on the same image was assessed for common carotid and femoral arteries. Variability was expressed as the coefficient of variation. Results: For common carotid artery, intraobserver intrasession variability was 7.9(SEM 1.6)% (ΔD/D), 4.5(1.1)% (D), 8.3(1.3)% (DC), and 9.1(2.6)% (CC), respectively. In femoral artery it was 12.4(2.2)% (ΔD/D), 2.7(0.6)% (D), 13.4(2.2)% (DC), and 12.5(2.1)% (CC). For brachial artery it was 13.4(2.8)% (ΔD/D). 2.5(0.5)% (D), 16.1(2.5)% (DC), and 15.6(2.6)% (CC). Intraobserver intersession variability was comparable to intraobserver intrasession variability for all vessels. Interobserver intrasession variability for common carotid artery was 11.3(2.6)% (ΔD/D) and 8.6(1.9)% (D), but was larger for DC and CC. Interobserver variability on the same image was Conclusions: In conclusion, the vessel wall movement detector system has a good technical reproducibility. Intraobserver intrasession and intersession variability are comparable, and are larger in muscular arteries. This might be due to a larger variation in tone of these arteries, which are under permanent neurohumoral control. Interobserver intrasession variability was larger than intraobserver variability and might be influenced by differences in observers' skill and spontaneous variation in vessel wall properties. Cardiovascular Research 1994;28:610-614