Abstract: A method of and apparatus for making the cable core of a telecommunication cable water-tight in the longitudinal direction, in which a filling material having a base of petroleum jelly is heated to a temperature above the drop point, is supplied under pressure to a filling head (5), is divided into a number of jets distributed over the circumference of the cable core, is passed through the filling head (5) with simultaneous conversion of the static pressure into kinetic energy and is injected through the outer layer of the cable core into the heart of the cable core, in which a reconversion of the kinetic energy into static pressure is effected and all the interstices and gaps between the single wires of the cable core are filled with the filling material.