The present invention relates to a method for controlling of a filtration rate during treatment of a body fluid, particularly during haemofiltration or dialysis of a patient by means of a respective device, comprising the steps of defining a target relation, or a development during dialysis thereof, between one or more calculated or measured value(s) reflecting the mass or the concentration or the volume of a substance comprised by a tissue or a bodily fluid of the patient, and one or more calculated or measured value(s) reflecting a distribution space of the patient or an approximation thereof； during dialysis repeatedly calculating or measuring of value(s) reflecting the mass or the concentration or the volume of the substance and/or reflecting the distribution space or an approximation thereof, and determining the relation there between at least once； and controlling the filtration rate of the body fluid treatment device such that the determined relation is or approaches the target relation or aims to do or be so. It also relates to a controller, an apparatus, a device, a digital storage means, a computer program product, and a computer program.
