The EPR spectra of Fe3+ in the three ferroelectric phases of BaTiO3 could be interpreted on the basis of the Newman superposition model. In the latter, the position of the nearest (oxygen) ligands determines the EPR spectrum. It is found that the Fe3+ participates by less than an order of magnitude in the collective motion of the Ti4+ ions out of their inversion symmetric position: by centering the Fe3+ and using previously determined intrinsic oxygen coordinates and parameters of the Newman model, the sign and magnitude of the EPR b20 terms could be obtained for (a) the tegragonal phase, (b) the tetragonal 001 spectrum perpendicular to the 110 polarization in the orthorhombic phase, and (c) the very small 111 splitting in the rhombic phase; the electronic polarization being of the same magnitude in all three phases. The centered Fe3+ also yields correct EPR b20 parameters for PbTiO3 and KNbO3. The investigation shows that the Fe3+ is a very sensitive probe of the intrinsic oxygen positions. The small coupling of the Fe3+ to the off-center ferroelectric motion is ascribed to its half-filled 3d shell. © 1979 The American Physical Society.