A retarder brake system of a vehicle combination including an agricultural tractor and an electrically driven trailer includes a drive train with a combustion engine, a vehicle transmission downstream from the combustion engine, a mechanical drive axle of the agricultural tractor connected to a first gear output of the transmission, a first electrical motor generator unit coupled to a second gear output, and an electrical drive axle of the trailer. The electrical drive axle is driven by means of a second electrical motor generator unit. The generator units are electrically connected with one another via a direct current link. In a retarder operation, the second electrical motor unit is operated with a generator and the first electrical generator unit is operated with a motor. At least part of the gross retarder output requested on the electrical drive axle is dissipatively destroyed as a power loss within the drive train.
