Abstract: A tester for a communications (e.g. telephone) line pair comprising a pair of different valued resistors (R1 and R2) each connected in series with a diode (D1 and D2). The diode/resistor pairs are connected in parallel between connectors (A and B) such that one of the pair provides a path for a DC voltage of one polarity and the other of the pairs provides a path for a DC voltage of the other polarity. The device is connected to the ends of a spare pair of telephone wires at a remote distribution point. The spare pair is provided with it's exchange equipment termination and testing is carried out at the local exchange via the test access facility to check that the pair of wires is in working condition before sending installers out in site. The test procedure includes measuring the total resistance of the lines to determine whether the difference in resistance readings as determined are in accordance with the difference between the resistances (R1 and R2) in the device itself.