Abstract: A method and apparatus are disclosed for tracing leaks in vivo which occur in an electrode device, such as a pacemaker or a defibrillator, the electrode device including an electrode cable containing an elongate, flexible conductor having an exterior covered with a layer of insulation and having an interior channel. A leakage tracing device which is simple in structure, and therefore inexpensive to make, and with which one or more leaks in an electrode cable implanted in a patient is/are readily detectable, has a tubular, flexible body within an external diameter smaller than inner diameter of the interior channel of the electrode cable. The tubular body can be inserted into the electrode cable's interior channel all the way to the channel's distal end, and the proximal end of the tubular body is connected to a container for a fluid.