Aniline was polymerized in the presence of ultrafine colloidal silica particles (hydrodynamic diameter 35 nm) in aqueous media and, given a sufficient silica concentration, colloidally stable polyaniline-silica particles were obtained. The particle size of the resulting dispersions was determined by both dynamic light scattering and disk centrifuge photosedimentometry. The typical size of these polyaniline-silica particles is in the range 300-600 nm and is insensitive to the concentration of components in the reaction mixture, temperature, or acidity of the reaction mixture. Particles produced at 0 degrees C are spherical and their shape becomes less defined when polymerization proceeds at 25 degrees C. As the silica size is increased, the composite particles become larger and their raspberry morphology more distinct. The electrical conductivity of a typical polyaniline (37.8 wt%)-silica composite is 6.1 x 10(-2) S cm(-1) at 25 degrees C. It grows with increasing temperature and does not depend on the frequency in the investigated range from 20 Hz to 1 MHz.