Abstract: A circuit arrangement is provided for testing a passive bus network system which comprises stations which are connectible to a coaxial cable segment via media adapter units, the stations realizing the data packet exchange via the coaxial cable segment with carrier sense multiple access with collision detection access method. In conjunction with a status receiving device which monitors the transmitted data packets, the passive bus network system is monitored by the data transmitter and the data receiver in view of the presence of the line terminating impedances, the proper connection of the media adapter units to the transmission medium, as well as the transmitting and receiving functions and the collision recognition and state of the collision recognition circuit.