A method to determine the surface anchoring energy of a nematic liquid crystal is proposed. The technique implies the measurements of optical retardation of a nematic cell as a function of a strength and direction of the applied magnetic field. It enables one to get both pretilt angle &agr; and anchoring coefficientWain the course of the same experiment. As an example, both parameters (&agr;=10.9° andWa=1.5×10−5J/m2) are measured at the interface between the nematic 5CB and rubbed polyimide film. ©1995 American Institute of Physics.