Employing photoemission electron, microscopy as spatially resolving method the existence range for pattern formation in the NO+H-2 reaction on Rh(110) has been determined. The boundaries between bistable and excitable regions and between different types of chemical wave patterns have been mapped out in pH(2), T-parameter space with fixed p(NO)=1.6x10(-6) mbar. (C) 1997 American Institute of Physics.