Amniotic sac puncture is a reliable procedure for induction of a cleft palate in rat foetuses 15 days old. 2) This possibility persists during the first hours of day 16. 3) When applied to rats after 16 days 12 hours of pregnancy, amniocentesis does't induce a cleft palate. 4) Treatment during this critical stage of pregnancy with substances able to reduce the amniotic fluid volume, such as acetazolamide and hydrocortisone, doesn't produce cleft palate.