In one example, a system for loading build material into a portable build unit having a platform on which objects are printed and a build material supply container next to the platform. The system includes a build material dispenser, a conveyor to move the build unit and/or the dispenser, and a controller operatively connected to the dispenser and the conveyor. The controller is programmed to, with the build unit and the dispenser in a fill position, cause the dispenser to dispense build material into the supply container, cause the conveyor to move the build unit and/or the dispenser to and/or from the fill position, and, while the conveyor moves the build unit and/or the dispenser to and/or from the fill position, cause the dispenser to dispense build material on to the platform.