Peripheral artery cannulation is a common procedure but can sometimes be difficult. Our goal was to determine if a median nerve block would increase the diameter and flow of the radial artery. Radial artery diameter and peak velocity was measured using a SonoSite Ultrasound System. Using ultrasound guidance, a median nerve block was performed with lidocaine. Subsequent measurements of the radial artery and peak velocity were again made at 5 minutes post-block and 10 minutes post-block. Mean radial artery diameter measured vertically was 0.23 ± 0.06 cm pre-block, 0.23 ± 0.05 cm at 5 minutes post-block, and 0.23 ± 0.05 cm 10 minutes post-block. Mean radial artery diameter measured horizontally was 0.26 ± 0.05 cm pre-block, 0.27 ± 0.06 cm at 5 minutes post-block, and 0.27 ± 0.08 cm 10 minutes post-block. Peak velocities were 11.3 ± 6.9 cm/s pre-block, increased to 15.0 ± 6.9 cm/s 5 minutes post-block (P = 0.005), and finally increased to 17.7 ± 7.8 cm/s 10 minutes post-block (P = 0.01). This study set out to measure the effects of median nerve blockade on the radial artery. We found a significant increase in peak velocities post-median nerve blockade.