type
  ParseThread = class(TThread)
  private
    { Private-Deklarationen }
     Form1: TForm1;
     i:integer;
    protected
    procedure Execute; override;
    procedure DoSomething;
   public
    { Public-Deklarationen }
     constructor Create(Form1: TForm1);
end;

var
  Form1: TForm1;
  tt: ParseThread;

implementation

{$R *.dfm}

procedure ParseThread.Execute;
begin
 while not Terminated do
   begin
     Synchronize(DoSomething);
   end;
end;

procedure ParseThread.DoSomething;
begin
     inc(i);

    form1.Memo1.Lines.Add(inttostr(i));

 if i = 5000 then begin
    i:=0;
    SuspendThread(tt.Handle);
 end;
end;

constructor ParseThread.Create(Form1: TForm1);
begin
  inherited Create(False);
  Self.Form1 := Form1;
end;

procedure TForm1.BitBtn1Click(Sender: TObject);
begin
 tt := ParseThread.Create(Self);
 tt.FreeOnTerminate := true;
end;

end.