The behaviour of cells within a tissue is controlled by the cell’s environment. Amongst the most important signals that cells receive are in the form of circulating small proteins called growth factors. These bind to specific proteins, called receptors, which are found on the surface of cells. Binding of growth factors causes the receptors to alter their pattern of interactions with many molecules inside the cell that control cell growth. In this way growth factor receptors relay information between the cell exterior and interior to stimulate so-called mitogenic responses, which enable cells to grow and divide. In order to prevent these responses continuing endlessly, which leads to uncontrolled cell division and eventually to cancer, the growth factor receptor must be hidden inside the cell and eventually destroyed. The aim of our work is to understand how activated mitogenic receptors follow the pathway from the cell surface to their site of degradation, and how the cell makes sure this transit occurs only when it has received sufficient stimulus from circulating growth factors.