δ18O analyses of water in the blood of domestic and wild pigs indicated that large isotopic differences exist between domestic and wild specimens of the same species (Sus scrofa) living in the same area. Similar isotopic differences are found between the δ18O(PO43–) values of bones from the two groups of animals. When δ18O values obtained from recent wild boar bones are introduced in the equation of the isotopic scale determined for domestic pigs, totally unreliable δ18O values of local meteoric water are obtained. The δ18O(PO43–) values measured in three groups of modern wild boar specimens allow the calculation of a first approximate equation which is quite different from that of domestic pigs. This isotopic scale should be accurately re-calibrated for wild animals. Copyright © 2011 John Wiley & Sons, Ltd.