The relations between the energy levels of 57Fe nuclei and the magnetic and electric hyperfine fields are analysed.The polar angles specifying the orientation of Heff with respect to the principal axes of EFG tensor and asymmetry parameter are expressed in closed form by the energy levels and the quantity e2Qq/[4I(2I−1)]. The expressions for the ranges of the allowed values of EFG parameters for a given set of energy levels are derived and discussed.