Ventilation effectiveness was measured on a prototype system for local air-conditioning named personal microclimate system (PERMICS). Based on simultaneous measurements of velocity field and of tracer gas concentration, a new parameter based on the relative decrease of tracer gas in the first minute of system operation was introduced. The usefulness of this parameter has been verified by simulation results from commercial computational fluid dynamics (CFD) software. This parameter makes quick measurements of the local efficiency of ventilation systems possible. (c) 2005 Elsevier B.V. All rights reserved.