Microsoft Forum: Passing parameter/variable to URL

Try this expression:

= "http://gisapps/ArcGIS10/rest/services/StreetBaseMap/MapServer/export?bbox="+Fields!ENVX1.Value +"%2C"+Fields!ENVX2.Value + +"%2C"+Fields!ENVX3.Value + +"%2C"+Fields!ENVX4.Value + "&bboxSR=&layers=&layerdefs=&size=&imageSR=&format=png&transparent=false&dpi=&time=&layerTimeOptions=&f=image"