AbstractOn the basis of the crystal‐field theory the zero‐field splitting andg‐values of the3A2ground state for d8impurity ions in a trigonally distorted octahedral field are calculated. Using perturbation theory the analytical expressions connecting the spin‐Hamiltonian parameters with the crystal‐field parameters are obtained. It is shown that experimental data for Cu3+in Al2O3, and Ni2+in Al2O3, α‐LiIO3, LiNbO3can be explained taking into account the influence of all the excited levels on the