The term pseudopregnancy was first used by Ancel and Bouin (1911) to describe an abnormally long luteal phase of the estrual cycle observed in the rabbit. Originally the term applied to the condition whereby, following copulation, no conception would take place, but that uterine and ovarian changes similar to those seen in pregnancy would ensue. It is now known that pseudopregnancy can occur in the virgin bitch following estrum when no copulation has taken place. It should be remembered that unlike the rabbit, ferret and other animals, the dog ovulates spontaneously, i.e., without the need of the copulation stimulus to cause the rupture of the follicle and consequent liberation of the ovum.