The uranium contents of thirteen rock reference samples from the Centre de Recherches Pétrographiques et Géochimiques, Nancy, France, were determined by delayed‐neutron activation analysis. Four others from the same laboratory were found to have uranium concentrations below our limit of detection. Meaningful comparison of our data with other workers is presently not possible (i) because of the paucity of uranium data and (ii) because of the disparity of uranium data on the samples for which uranium data ex