Spin Hamiltonian parameters for a ferromagnetically coupled dinuclear Ni(II) complex [Ni-2(en)(4)Cl-2]Cl-2: J = +9.66 cm(-1), g = 2.242, D-A = -4.78 cm(-1), D-AB = -0.64 cm(-1) and zj = -0.402 cm(-1) were reliably determined from a powder sample by simultaneously fitting them to magnetic data and tunable-frequency high-field EPR resonances. The importance of employing both techniques is underscored in view of the weak-exchange limit in this particular system. The parameters and the novel methodology developed in obtaining them will serve to better understand magnetic properties of more complicated transition metal clusters.