Now it can be said with certainty: what goes in, does come out, at least with regard to carbon nanotubes and mice. But, the ramifications fall more in the realm of biomedicine than Newtonian physics. The newfound knowledge alleviates concerns that nanotubes used to deliver medicine might linger in the organs after their job was done and eventually prove toxic. The findings pave the way for further research into biomedical applications of carbon nanotubes.