Abstract: For the conditioning of ion exchange resins, pure water is recirculated over a bed of the resin to be purified or of the resins to be purified. The pure water has a residual salt content of less than 50 ppb and a content of free acids or free bases of less than 5,000 ppb. The organic and inorganic substances washed out of the resin or the resins are removed continuously from the circulating water by methods for the purification of water. The process can be used for conditioning the ion exchange resins used in an ultra pure water production system.