The hydrolysis of 0.06 mol dm(-3) Fe(NO3)(3) solutions was followed at 65 degrees C by means of pH and dynamic light scattering measurements. The hydrolysis products were characterized by transmission electron microscopy and nitrogen adsorption. Depending on the heating procedure different phases were observed, i.e. alpha-FeOOH (goethite) was formed on heating a 0.06 mol dm-3 solution to 65 degrees C, and alpha-Fe2O3 (hematite) if an appropriate amount of a concentrated stock solution was added to the preheated water at 65 degrees C. An explanation of this behaviour is offered by taking into account the possible formation of quite different structural units of both solid phases in the course of the hydrolysis process.