A method and apparatus for data exchange between a towing vehicle and an attached trailer uses radio contact via transmission/receiving modules contained in the towing vehicle and in the trailer. To recognize that the towing vehicle and the trailer are connected, the transmission/receiving module of the towing vehicle transmits an identification signal, and at the same time, changes the electrical status of a connection line between the towing vehicle and the trailer. If the transmission/receiving module located in the trailer recognizes the change in the electrical status of the connection line simultaneously with receiving the transmitted identification signal, the identification signal is stored within the trailer. In subsequent communications between the towing vehicle and the trailer, the identification signal is always transmitted before the message. As such, only the attached trailer, with the appropriate stored identification signal, can communicate with its towing vehicle. Moreover, the same technique can be used for multiple trailers attached to the same towing vehicle.