a b s t r a c tBased on experimental data it is shown, for some chosen alloys and compounds of iron, that there is no unique relationship between the 57 Fe-site magnetic hyperfine field, B hf , and the magnetic moment per Fe atom, . Instead, the B hf -plot consists of several branches, each of them being characteristic of a given alloy or compound. Consequently, the effective proportionality constant (hyperfine coupling constant) depends on the alloy system or compound, and for a given alloy system or compound it depends on the composition or even on the lattice site. Consequently, the scaling of B hf into the underlying cannot be done a priori.