The first highly resolved 27Al NMR spectra of alkaline aluminosilicate solutions have been recorded and are discussed. The linewidths and number of resolved lines are shown to depend critically on several factors, especially the pH and Si∶Al ratio. At least thirteen separate peaks or bands are observed at pH ≈ 10.35 and Si∶Al = 1∶1. A substantial range of anionic species, comparable to those found for alkaline silicate solutions, is thus shown to exist in dynamic equilibrium. Tentative assignments of some bands are presented, based on 27Al and 29Si shift comparability, 27Al linewidths and 27Al spin–lattice relaxation measurements. Relative intensities of the various 27Al signals are given for the pH ≈ 10.35 solution.