The complex dielectric permittivity of concentrated aqueous alkaline aluminate solutions at total concentrations 1 less than or similar to [Al](T)/mol dm(-3) less than or similar to 6 with either [Na](T) 8.33 mol dm(-3) or [Al](T)/[Na](T) = 0.750 has been determined at 25 degreesC in the frequency range 0.5 less than or similar to v/GHz less than or equal to 20. All solution spectra could be represented as a superposition of a Cole-Cole relaxation-time distribution for the solvent relaxation with an additional low-frequency Debye dispersion assigned to the solute. The variation of the effective hydration number, deduced from the water dispersion amplitude, shows that the aluminate ion, Al(OH)(4)(-), is less strongly solvated than the hydroxide ion, OH-. Additionally, a "melting" of the hydration shells is observed at high concentration, probably due to co-sphere overlap and/or packing effects. The features of the solute relaxation are consistent with solvent-shared ion pairs of Na+ with a previously proposed dimeric anion, [(HO)(3)Al-O-Al(OH)(3)](2-). However, the data are not sufficient for an unequivocal assignment.