Try to use the mergeNewParams method on your layer http://dev.openlayers.org/docs/files/OpenLayers/Layer/WMS-js.html -- View this message in context: http://osgeo-org.1560.n6.nabble.com/Filter-on-WMS-Polygon-Layer-tp5044815p5044833.html Sent from the OpenLayers Users mailing list archive at Nabble.com.