The deposition of ferromagnetic microstructures on top of a high-mobility two-dimensional electron gas (2DEG) allows the investigation of electron transport in a periodic magnetic field which alternates on a length scale small compared to the elastic mean free path of the electrons. The longitudinal resistance of the 2DEG displays, as a function of the externally applied field, the long-predicted magnetic commensurability oscillations which result from the interplay between the two characteristic length scales of the system, the classical cyclotron radius Rc of the electrons and the period a of the magnetic field modulation.