In a method to determine a kidney function parameter of kidneys of an examination person with the aid of magnetic resonance tomography, at least one magnetic resonance measurement is implemented for an examination region of the examination person that comprises a urinary bladder of the examination person, to acquire magnetic resonance data from the examination region that include at least image data. The concentration of a urophanic substance in the urinary bladder of the examination person is automatically determined based on the acquired magnetic resonance data. A volume of the urinary bladder is automatically determined based on the acquired image data. A kidney function parameter of the kidneys of the examination person is automatically determined on the basis of the determined concentration of the urophanic substance in the urinary bladder and of the specific volume of the urinary bladder.