Pure magnetite nanoparticles (Fe3O4) have been synthesised in water by coprecipitation using two different approaches (from ferrous sulphate and a mixture of ferrous and ferric chlorides). All materials aggregated in aqueous suspension, but their subsequent dispersion on treatment with a variety of agents was observed to be different. Magnetite produced using ferrous sulphate could not be disaggregated, whereas magnetite produced from a mixture of ferrous and ferric chlorides could be disaggregated to a quasi-monodispersed form. The dispersing agents were tetramethyl ammonium hydroxide, Disperbyk 190 and polyacrylic acid. The finding has potentially important implications for the surface activation of superparamagnetic magnetite nanoparticles and their ability to be used in bio/life science applications.