using System.Threading;

       public delegate void MyInvoke(string str);
        private void btnStartThread_Click(object sender, EventArgs e)
        {
            Thread thread = new Thread(new ThreadStart(DoWord));
            thread.Start();
        }
        public void DoWord()
        {            
            MyInvoke mi = new MyInvoke(SetTxt);
            BeginInvoke(mi,new object[]{"abc"});                
        }

        public void SetTxt(string str)
        {
            txtReceive.Text += str + System.Environment.NewLine;
        }