High-field, multifrequency EPR data are presented for vanadium(III)-doped CsGa(SO4)(2).12X(2)O, where X = D or H, which afford the direct determination of the spin-Hamiltonian parameters pertaining to the (3)A(g) (S-6) ground term. A pronounced change in the g values and zero-field splitting is observed upon isotopic substitution which cannot be simply explained using a conventional ligand field model.