A high-precision radionuclide monitoring site was established in Yellowknife/Canada in 2003. Far away from nuclear activities, regular signals of 137Cs were found there during the summers of 2003 and 2004. We show that these signals can be explained by transport from fires burning in the boreal forests of North America and Asia. This finding has important implications. It demonstrates that 137Cs deposited world-wide from past nuclear testing is re-injected into the atmosphere by combustion to a significant extent and on a large scale, and is subsequently transported across great distances. Besides this, the analysis shows how efficiently a new receptor-oriented atmospheric transport modeling technique can be used to check whether a 3D emission inventory is consistent with discrete point measurements.