An effective fitting strategy in the directional ARMAX model-based approach is proposed for the rotor dynamics identification. The strategy is based on a priori knowledge of the degree of anisotropy in rotor systems gained from directional frequency response estimates. In addition, the anisotropy contribution factor is introduced in an effort to quantify the degree of system anisotropy. Finally, the applicability and effectiveness of the proposed strategy are investigated experimentally. (C) 1997 Academic Press Limited.