A large area (50 cm(2)) particle counter working under vacuum (10(-7) mbar) has been developed at CERN and applied to measurements of particles released by several vacuum components like valves, gauges and ion pumps. This technique has also been applied to study the migration of particles under vacuum with and without an applied electric field. This counter, which is based on the scattering of laser light by particles, is described with comments on the technical choices. The results of the contamination released by vacuum components and the effects of an electric field will be presented. (C) 1999 Elsevier Science Ltd. All rights reserved.