From https://en.bitcoin.it/wiki/API_reference_(JSON-RPC)#Controlling_Bitcoin

Bitnet Example (.NET Wrapper for bitcoind)

     BitnetClient bc = new BitnetClient("http://127.0.0.1:8332");
     bc.Credentials = new NetworkCredential("user", "pass");
 
     var p = bc.GetDifficulty();
     Console.WriteLine("Difficulty:" + p.ToString());
 
     var inf = bc.GetInfo();
     Console.WriteLine("Balance:" + inf["balance"]);