Abstract: Leakage of the cooling liquid in blast furnace nozzles is detected by measuring variations in the differential pressure of the cooling liquid using an electronic information system with the technology normally employed in inductive-type systems and capable of detecting minor liquid leakages which are not detectable with conventional control devices. Detection assemblies are incorporated at the cooling liquid inlet and outlet circuits of the installation. Each detection assembly includes a cylindrical housing surrounding a fixed annular hood having a double wall filled with mercury which serves as a guide for the displacement of a movable hood which is inverted with respect to the fixed hood, and provided with a counterweight and an axially projecting stem, the free end of which incorporates a core of magnetic material housed in the influence zone of the high frequency inductive circuit.