In a magnetic resonance marking system marking a flowing medium in a marking region, as well as in a magnetic resonance system with such a magnetic resonance marking system, a method to control a magnetic resonance marking system, and a method to generate magnetic resonance exposures, a radio-frequency transmission device generates marking radio-frequency signals, and a marking radio-frequency transmission coil emits the marking radio-frequency signals in the marking region. A magnetic field determination device determines a magnetic field strength in the marking region, and a control unit derives a marking transmission frequency from the determined magnetic field strength and to control the radio-frequency transmission device so that marking radio-frequency signals at the derived marking transmission frequency are emitted by the marking radio-frequency transmission coil.