The effect of weak low-frequency magnetic field on intracellular Ca(2+)-dependent proteinases (calpains) of fish and invertebrates was studied in in vivo and in vitro experiments. It has been found that intravital effect of weak low-frequency magnetic field tuned to the parametric resonance for Ca2+ ions led to a significant decrease in calpain activity in examined animals. It was shown that preparations of Ca(2+)-dependent proteinases from invertebrates and fish have been also substantially inactivated at the effect of indicated factor. Observed phenomenon is in the correspondence with an interference model of the impact of weak low-frequency magnetic field on the biological objects.