A cam treatment to reduce the friction coefficient thereof relative to a counterpart in an area provided with a hard coating made from amorphous Diamond-Like Carbon or DLC, involves disposing the cams on a support, bringing the support and the cams into a chamber placed under vacuum so as to clean the cams, bringing the support into relative movement along a trajectory of travel relative to a coating source, and taking the cams off the support before assembling them on a camshaft; the method involves disposing the cams on the support in a fixed configuration which is defined in such a way that the cams are brought successively opposite the source with orientations and at distances substantially identical relative to the source, to deposit a hard coating made from amorphous Diamond-Like Carbon or DLC, selectively on the fraction of the section of the cams that is oriented towards the source.