function validateForm() {
  var content = "Vul a.u.b. de volgende velden in:\n";
  validity = true;
  var frm = document.agenda_form;
  if (frm.Naam.value == "") {
    content = content + "- Uw naam\n";
    validity = false;
  }
  if (frm.Organisatie.value == "") {
    content = content + "- Organisatie\n";
    validity = false;
  }
  if (frm.Telefoon.value == "") {
    content = content + "- Telefoon\n";
    validity = false;
  }
  if (! validity) alert(content);
  return validity;
}