In situ room-temperature transmission Mossbauer spectroscopic study of precipitates formed in Fe-57(III)-containing highly alkaline electrolytes has been carried out after different periods of their ageing in the same solution. After 3.5 years of ageing an intensive resonant absorption was detected in the form of a single line. The latter effect has not been observed earlier for solid iron(III) hydroxo derivatives which have commonly been expected to give either quadrupole or hyperfine magnetic splitting. The precipitate aged for 15 months was found to give an essentially lower Mossbauer effect. After complete hydrolysis in water both products gave comparably intensive quadrupole-split doublets with distinctly different parameters owing to differences in the structures of the initial phases. The absence of quadrupole splitting for the 3.5-year-aged product is interpreted in terms of the formation of the cubic symmetry of the ferric ion coordination polyhedron in sodium hydroxoferrate(III), slowly forming in the course of long-term storage in highly alkaline medium, while at earlier stages of ageing, the precipitate consists of a labile, possibly intermediate, phase (eg ultrafine alpha-FeOOH particles) characterized by a low recoilless absorption probability. The results obtained are considered in relation with the processes occurring in alkaline storage batteries and electrolysers. Some effects leading to Mossbauer linewidth broadening, which may in principle take place in strongly alkaline electrolytes containing ferric derivatives with a symmetric hydroxo coordination, are also discussed.