An adaptive electronic transmission signal cancellation circuit for separating transmit data from receive data in a bidirectional communication system operating in full duplex mode is disclosed. The output of a main transmitter responsive to a first bias current is connected to the output of a receiver through an internal resistor. A first replica transmitter responsive to a second bias current and matched to the main transmitter current gain and rise/fall time characteristics is connected to the input terminal of the receiver, and produces a cancellation voltage between the output terminal of the main transmitter and the input terminal of the receiver as a function of the second bias current and the internal resistor. A second replica transmitter matched to the current gain and rise/fall time characteristics of the main transmitter and the first replica transmitter and responsive to the second bias current is connected to the output terminal of the main transmitter for canceling excess current, developed by the first replica transmitter, at the output terminal of the main transmitter.