Method and apparatus for transmitting a transmission signal via a two-core line, in particular a telephone line, in which case, with the aid of corresponding transmission devices (2, 3), two partial signals are generated and are transmitted via a respective core (A, B) of the line and the transmission signal is formed by the alternating-current difference between the two partial signals. In order to suppress common-mode components in the partial signals, a calibration is carried out in such a way that the transmission devices (2, 3) output essentially the same output level.