A flexible, body-implantable lead section which can be employed as an integral part of a monoplanar electrode system or alternatively as a separate means used to convert bipolar electrode system to a monopolar system. The lead section has at least one electrical conductor. The conductor is covered substantially over its entire length with an insulating material substantially inert to body fluids and tissue. The distal end of the conductor is adapted to be connected to an active electrode adapted to be located at a selected location inside the body. Indifferent electrode means are also provided. The indifferent electrode means are secured to at least a portion of the length along the surface of the inert material. In the preferred embodiment the indifferent electrode means is securely wrapped around at least a portion of the length of the inert material. This lead section with the indifferent electrode means can be employed with various configurations active electrodes for monitoring electrical activity and/or stimulating various types of tissue, including muscle and nerve tissue.