Polyaniline dispersions are obtained when aniline is oxidized in an acidic aqueous medium with ammonium peroxodisulfate in the presence of hydroxypropylcellulose. The progress of aniline polymerization has been monitored by the acidity changes and the formation of colloidal particles by dynamic light scattering. Submicrometre spherical polyaniline particles of good uniformity in size are produced at 0 degrees C, while at 40 degrees C the resulting objects have coral-like cylindrical morphology. A similar change of particle shape has been achieved at 0 degrees C by the acceleration of polyaniline formation by addition of a mediator, p-phenylenediamine. The concept of the formation of spherical and non-spherical morphologies and the role of the autoacceleration effect in the dispersion polymerization of aniline are proposed. Polymerization in the frozen reaction mixture at - 25 degrees C yielded a macroporous composite.