Paramagnetic resonances were observed in natural single crystals of anatase and are interpreted as due to regular substitutional Fe3+(I) and to Fe3+ combined with an oxygen vacancy at a nearest neighbour site (II). The observed unusually strong temperature dependence of the spin-Hamiltonian parameter b20 of (I) and the temperature dependence of the orientation of the magnetic axes of the spectrum (II) are both explained by assuming a shift within the unit cell of the equilibrium positions of the oxygen ions with temperature. © 1971.