Abstract: A circuit and method for sensing and compensating for longitudinal (common mode) signals in a subscriber loop of a telephone system. The circuit and method may include a longitudinal amplifier for sensing a difference between a reference voltage, V.sub.BAT /2, and a longitudinal voltage in the subscriber loop, and for providing four currents, two to each of two current amplifiers in the telephone system subscriber line interface circuit (SLIC). The longitudinal amplifier includes two current mirrors, each for providing two currents of the same polarity and of the same magnitude. The magnitude of the difference between the two currents being provided to each of the current amplifiers is proportional to the voltage difference. When compensation of the longitudinal signals has been achieved, the two voltages are the same and the magnitudes of the four currents are the same.