The ability to unequivocally identify the chemical nature of specified adatoms with the atom-probe field-ion microscope is demonstrated for the first time. Design features essential to this capability are discussed together with the underlying experimental techniques. The He ions used to image a given atom at a surface follow a path different from that of the field-evaporated surface atom itself. This results in an aiming error, which has been measured in our surface atom probe. Experiments with Rh atoms adsorbed on the (110) plane of W indicate that the atom probe is capable of identifying individual adatoms with a spatial resolution as good as, or better than, the resolution of the field-ion microscope.