Abstract Rubidium chemisorbs amorphously on Ag(111) at coverages below one monolayer, but ordered structures are formed in the multilayer regime. For thin layers the Rb grows as an fcc crystal, but above a certain critical thickness a phase transition occurs to yield the ordinary bcc form. The reactivity of Rb-dosed Ag towards NO is examined and compared with earlier work on Ag/Na. Although there are broad similarities between the two systems, certain important differences in chemical behaviour are found. These are mainly the result of reduced penetration of the Ag lattice by Rb, and the very greatly reduced surface → bulk transport of chemisorbed oxygen as compared with the case of Na. Evidence is also found for the formation of surface compounds between Rb, O, and N on Ag(111), and auxilliary experiments with O 2 and N 2O are carried out in an attempt to shed further light on the nature of these compounds.