The reactions of Rh+ with CH4 have been studied by using guided ion beam mass spectrometry. Ionic products, RhH+ and RhCHx+ (x = 0-3), are all formed in endothermic processes. The dehydrogenation reaction to form RhCH2+ is the lowest energy process observed, while at high energies, RhH+ dominates the product spectrum. The reaction mechanisms and the potential energy surfaces for the CH4 system are discussed. In contrast to theoretical studies, we find that there is no barrier in excess of the endothermicity for the dehydrogenation reaction. The reactions of Rh+ with methane are compared with those for Co+ + CH4, and the differences are rationalized in terms of differences in the metal orbitals used in the bonding and the electronic structures of the metal-methylidene product ions.