var str = "http://serverapps.esri.com/SilverlightDemos/ProxyPage/proxy.ashx?http://sampleserver3.arcgisonline.com/ArcGIS/rest/services/HomelandSecurity/operations/FeatureServer/2?f=pjson"; WebClient w = new WebClient(); w.DownloadStringCompleted+= (s, e) => { }; w.DownloadStringAsync(new Uri(str, UriKind.Absolute));