We present first results of a detailed study by both PAS and ESR of the influence of preparation conditions and stoichiometry on the defect chemistry of BaTiO(3) and of more complex perovskites with the general formula Ba(B'(1/3)B"(2/3)), where B' = Mg, Zn, Ni, and B" = Nb, Ta. In BaTiO(3), several paramagnetic defects such as, Ti(3+), V(Ba), and V(Ti) were detected and identified by ESR, and correlated with positron lifetime data. In the more complex perovskites, the positron data are significantly more difficult to interpret and show a strong dependence on the density of the sintered material.