Specifies the requirements for the laboratory testing of the resistivity of specially prepared specimens of plastics made conductive by the incorporation of carbon black. The test is suitable for materials having a resistivity of less than 104 Ohm x m. A stable d.c. current is passed between electrodes at the ends of a test piece. A schematic diagram of the test circuit is given. The voltage drop between the two potential electrodes, set on the test piece while the current flows, is measured with an electrometer. The resistance of the portion of the test piece between the potential electrodes is independent of contact resistances.