The rare isotopes236U and239Pu are produced naturally by neutron capture in uranium ores. Here we measure236U and239Pu by accelerator mass spectrometry (AMS) in the same ore samples for the first time. To ensure efficient extraction of both elements and isotopic equilibrium between the239Pu in the ore and a242Pu spike, we developed a new sample preparation protocol. AMS has clear advantages over previous methods because it achieves better discrimination against molecular interferences with higher sensitivity and shorter counting times. Measurements of236U and239Pu hold considerable promise as proxy indicators of neutron flux and uranium concentration. © 2007 Elsevier B.V. All rights reserved.