A device for treating magnetizable or magnetically attractable particles which are present in a liquid, comprising a holder for one ore more reaction vessel(s) with the liquid containing the particles, at least two movably arranged permanent magnets, a drive unit for moving the permanent magnets; with the permanent magnets being arranged in pairs and opposite each other, and being movable in vertical direction (a, b), and the distance between the two permanent magnets of a pair being dimensioned or adjustable such that a reaction vessel can be positioned therebetween.