Corrosion mechanisms induced by chloride contamination and injection defects are the main causes of degradation of the prestressed concrete structures. Recently, a new technique has been developed for the treatment of the prestressed rebars. It is based on the injection of a corrosion inhibitor by an ultrasonic pump directly into the grout by means of holes drilled through the concrete covering the duct. At the end of the injection, an additional grout is also introduced in the duct in order to fill initial injection defects. This technique seems very attractive as it may ensure the contact between the inhibitor and the rebar. In order to evaluate its efficiency and its durability, several tests were performed during a research program. In a first step, the propagation of the inhibitor solution in the grout was evaluated. Several representative compositions were tested and two injection techniques were compared: the ultrasonic technique and a second one using only an injection pressure. In a second step, the efficiency against corrosion was evaluated. Concrete samples containing tendons inserted in metallic ducts were cast. These ducts were filled by a grout contaminated with several chloride concentrations. After the injection of the corrosion inhibitor, several analyses were performed over one year: the corrosion activity was recorded, the rebars were inspected by sample autopsies and the presence of the corrosion inhibitor was sought.