In a method for longitudinal sealing of electrical lines (2), which have one or more line fibres (21) arranged in an outer sheath (22), and cavities (23) between the individual line fibres (21) as well as between the individual line fibres (21) and the outer sheath (22), that end (2a) of the line (2) to be sealed is, according to the invention, immersed in a liquid sealing compound (3), and a reduced pressure is applied to the other end (2b) of the line (2). A sealing apparatus (1) that is suitable for carrying out this method has a supply reservoir (4) for the liquid sealing compound (3), in which the end (2a) of the line (2) to be sealed is immersed, and a vacuum-pressure source (5), to which the other end (2b) of the line (2) is connected.