A device for manipulating communication messages in a communication system is provided, which communication system includes a data bus, and a plurality of nodes connected thereto, and an arrangement for transmitting messages in message frames at fixedly predefined communication cycles. The device is connected in the data bus between at least one node for which the messages to be manipulated are intended and the other nodes of the communication system. The device has an arrangement for intercepting the messages before they reach the at least one node, an arrangement for manipulating the intercepted messages, and an arrangement for transmitting the manipulated messages to the at least one node.