Electron paramagnetic resonance (EPR) spectra of Ni-doped gallium borate show a surprisingly pronounced dependence of certain line intensities on the orientation of the microwave field B 1 with respect to the crystal axes. In order to account for this dependence, we have considered in detail the B 1 caused perturbation matrix and obtained an expression of the angular dependence of transition probabilities between spin levels. Computer-generated EPR spectra taking into account this dependence provide good fits to the experimental spectra characteristics.