Dilute magnetic semiconductors and wide gap oxide semiconductors are appealing materials for magnetooptical devices, From a combinatorial screening approach looking at the solid solubility of transition metals in titanium dioxides and of their magnetic properties, we report on the observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8%, Magnetic microscopy images reveal a magnetic domain structure in the films, indicating the existence of ferromagnetic long-range ordering, The materials remain ferromagnetic above room temperature with a magnetic moment of 0.32 Bohr magnetons per cobalt atom, The film is conductive and exhibits a positive magnetoresistance of 60% at 2 kelvin.