A single crystal X-ray diffraction study of the new compound [Rb([2.2.2]crypt)](2) [Rb([18]crown-6)][HGe9]center dot 4NH(3) revealed the presence of the first protonated nine-atom germanide cluster [HGe9](3-). It forms from Rb4Ge9 in liquid ammonia, so that [Ge-9](4-) can be considered as the base and [HGe9](3-) its formally conjugated acid. The H atom is attached to a germanium vertex atom of the basal square plane, as it is known for [RGe9](3-) (R = C5H9 , Mes, etc.) or [HEX9](3-) (E = Si, Sn). In addition, the proton could be located unambiguously in the Fourier difference map. [HGe9](3-) also represents a nido cluster species with 22 cluster-bonding electrons, which can be considered the most stable structure for nine-atom cluster species for all group 14 elements.