Vascular development and angiogenesis are known to be regulated by various signals, but the roles played by blood flow and biomechanical signals are unclear. This is mostly because the ability to image and measure changes in blood flow has been limited. Now, Elizabeth Jones and colleagues develop a method to simultaneously image blood flow dynamics and vascular remodelling (p. 4158), and use this technique to show that flow dynamics control sprout location and elongation in quail embryos (p. 4151). Their imaging approach uses micro-particle image velocimetry: embryos are injected with a fluorescent dye that labels endothelial cells and with fluorescent microspheres that act as tracers of fluid motion. Subsequent imaging via a high-speed camera allows changes in blood flow dynamics and vessel geometry to be quantified. Using this method, the researchers demonstrate that sprout location can be predicted based on flow dynamics; sprouts form from vessels that are at a lower pressure towards vessels at a higher pressure and localise to points where shear stress, a force created by flow, is at a minimum. In addition, the rate of sprout elongation is proportional to the pressure difference between the two vessels. These studies provide insights into the hemodynamic forces at play during vascular development and open the door to further studies of the biomechanical control of vascular remodelling.