The average charge of insulating polymer particles has been measured as a function of particle size and tribo‐electric treatment of the sample. Particle sizes were in the range 5–30 &mgr;; the particle size distribution was determined by means of a light microscope. The charges were measured with an electrometer: the particles were supported on a photoconducting layer and the electrometer measurements were made in the dark and in the light; thus, the position of the ground plane was effectively varied, and by comparing the two sets of results the average distance of the particle charge from the photoconductor surface could be inferred. Average charges as large as 4×105electrons per particle were measured.