Both hydrogen and natural gas engines with an effective power of more than 400 kW can be tested under transient operation with the recently developed test bench. By means of the Road Load Simulation software package the longitudinal vehicle dynamics can be investigated already on the engine test bench. Furthermore, any driving cycles can be defined and redriven afterwards. The hydrogen storage volume allows several hours of full-load operation of heavy-duty truck engines. This paper only concentrates on the hydrogen-specific features and hardware of the test bench.