The control of particle size by external electric fields is investigated during flame synthesis of particles at high production rates (up to 87 g h(-1)). Here needle and plate electrodes are used during synthesis of fumed silica from hexamethyldisiloxane (HMDS) in a coflow double diffusion flame at atmospheric pressure. The average primary particle diameter is reduced by a factor of two, when the applied electric field strength between two needle electrodes was increased from 0 to 1.5 kV cm(-1) . It was demonstrated that electrode placement is crucial for this process. Furthermore, the powder composition (soot content less than 1 wt%) was controlled by the electric field.