By means of high-resolution scanning tunneling microscopy (STM), we studied the adsorption and reaction of submonolayer NH3 on rutile TiO2(110) surfaces in different oxidation states. On a clean, reduced TiO2(110) surface with O vacancies, NH3 adsorbs at 120 K exclusively as single molecular species on surface Ti sites. On a TiO2(110) surface with H adatoms, we observed small amounts of NH3 monomers in close proximity to each other and NH3 dimers, in addition to the majority of isolated NH3 monomers. On such a surface, we found that NH3 and H adatoms can diffuse together along the [001] direction and NH3 can diffuse along the [11¯ 0] direction via "hydroxyl bridges". On an oxidized TiO2(110) surface with O adatoms (Oot) and O2 molecules, we found dimeric NH3 species and isolated OHt groups. Interestingly, there were also grouped adsorbates of NH2OH stoichiometry (singles and pairs). Following annealing at 330 K, the coverage of paired NH2OH species was much increased. We find a strong affinity of NH3 species to interact with Oot adatoms and Oot adatom pairs and propose dissociation of NH3 species at Oot adatoms. Finally, we discuss the faith of the observed adsorbates at elevated temperature.