uses FileCtrl; 
 
function GetRP(const basis, ziel: string): string; 
  function bslash(const s: string): string; 
  begin 
    result := s; 
    if ansilastchar(result) <> '\' then result := result + '\'; 
  end; 
begin 
  if (directoryexists(basis)) and (directoryexists(ziel)) then 
    result := ExtractRelativePath(bslash(basis), bslash(ziel)) 
  else result := ''; 
end; 
 
// Beispielaufruf 
 
procedure TForm1.Button5Click(Sender: TObject); 
var s: string; 
begin 
  s := GetRP('C:\Dokumente und Einstellungen', 'C:\Windows'); 
  if s = '' then showmessage('FEHLER') else 
    Label1.caption := s; 
end;