An arrangement and a method for producing high-purity crystals, such as temperature-sensitive pharmaceutical agents, in a countercurrent crystallization process. The arrangement comprises a plurality of crystallizers, mother liquor lines, each of which has a shut-off valve, and crystallization product lines, each of which has a shut-off valve, so that a mother liquor flow can be generated which is directed from a crystallizer to the second-next crystallizer in the direction of decreasing purity, and a crystallization product flow can be generated which is directed from a to dissolved crystallization product that is about to crystallize to the next crystallizer in the direction of higher purity.