A mechanism that describes effects of a pulsed magnetic field PMF of ELF range on some biological systems is presented. This Ž .
mechanism, based on earlier proposed ion interference mechanism, links the dissociation probability of ion-protein complexes to
parameters of PMF. Quantum dynamics of ion is studied in the case of PMF combined in line with a static magnetic field. A rule that
enables us to reach a maximal biological response on PMF is found. The formula is derived for the first time for biological efficacy of a
PMF. Calculations were made for Ca- and Mg-protein complexes. The results show a good consistency with known experimental data.