Surface roughness of metal counterface is an important parameter in the wear process of acetal-metal gear pairs. The topic of this paper is whether the results obtained from pin-on-disc or pad-on-disc machines are valid in real operating conditions, i.e. in the machine itself. For this purpose the wear of acetal-metal gear pairs at different counterface roughnesses in a real device was studied. It was shown that the wear rate and the type of wear were influenced by surface roughness of the metal counterface.