X-ray absorption of oxygen is significant in thin specimens of Pb(Mg1/3Nb2/3)O-3-35 mol% PbTiO3 [PMN-35PT] due to the presence of heavy elements such as Pb and Nb. Therefore, direct measurement of the oxygen concentration in these types of systems can be difficult. Furthermore, assumption of the composition from stoichiometric considerations may not be feasible, particularly if the valence state of one or more of the cation species is variable. Using only XEDS data, the zeta-factor method provides absorption corrected compositional information. In the present study, it was shown that such data were in very good agreement with the nominal values for PMN-35 PT, whereas the uncorrected data underestimated the oxygen content by 300%. In previous work, it was theorized that the swelling of samples containing excess PbO was linked to changes in the composition of the intergranular liquid phase. The zeta-factor technique was used to show that the oxygen to lead ratio of this second phase changes upon annealing. (C) 2004 Kluwer Academic Publishers.