Abstract: Asbestosis is a disease provoked by fibers. The nanowires widely used in nanotechnology, including carbon nanotubes and metallic nanowires, could be just as toxic. Silver nanowires can create conformal and flexible percolation networks in electrically conductive, and optically transparent films increasingly used in displays and touchscreens. The health risks of silver nanowires can only be assessed by fundamental research on their cellular uptake and physiological impacts. I will present experimental results from an international collaboration I established to discover principles of nanowire interactions with living cells. By combining X-ray and optical microscopy, and molecular probes of endocytosis and dysfunction in cells, we demonstrate a new biophysical threshold for fiber pathology.