Accessing web service using post method in ASP.Net

string URI = "http:xxx.xx.xxx.xxx:xx/customerEnergy/Login.asmx/ValidateLogin";
string myParameters = "UID=admin&Password=password";

using (WebClient wc = new WebClient())
{
wc.Headers[HttpRequestHeader.ContentType] = "application/x-www-form-urlencoded";
string HtmlResult = wc.UploadString(URI, myParameters);
}