An arrangement for simultaneous two-way data transmission of data signals with a given symbol frequency over two-wire circuits of a type found in telephone networks or of a comparable type. The arrangement comprises an echo canceler with an adaptive filter for producing from transmit channel signals approximated echo signals which are differentially combined with receive channel signals for forming substantially echo-free residual signals. A special type of code conversion is employed in the transmit channel, whereby p-level data symbols are converted into modified p-level data symbols which are thereafter converted into (2p-1)-level data symbols. The echo canceler comprises a digital adaptive filter to which the modified p-level data symbols and the residual signals with a sampling frequency equal to the symbol frequency are supplied. These measures result in a transmission signal having favorable spectral properties, a simple inverse code conversion and an echo canceler which combines simplicity of implementation with favorable convergence properties.