The valence bands of ultrathin Fe and Co layers deposited on a Cr(100) surface at room temperature are studied by ARPES and UPS. Transitions from Fe minority and majority spin bands are still observed for coverages of about 1 monolayer, showing that Fe remains ferromagnetic. These studies agree with theoretical calculations which predict an enhanced magnetic moment for ultrathin Fe layers on Cr(100). Measurements on Co layers let us suppose that a Stranski-Krastanov growth mode occurs, with a bcc Co phase for the very first layers.