The effect of the selective influence of a dc magnetic field on the characteristics of nominally pure triglycine sulfate crystals was detected for the first time. A short (minutes) exposure to a weak magnetic field B ₀=0.08±0.01 T caused long-term (hundreds of hours) changes in the spontaneous polarization, coercive field, Curie temperature, and permittivity of the crystal at the Curie point. The effect is selective in nature presumably because of the participation of hydrogen bond protons in the spin-dependent processes of the transformation of defect complexes in real crystals.