AbstractImmature, pregnant andpost partumrabbits were used to study the mechanical function of the uterotubal junction in the accumulation of the luminal fluid in the ligated uterine tube. Does were laparotomized at 10 hours, 2, 3, 4, 5, 7, 9, 16 and 29 dayspost coitum.One uterine tube was ligated at the fimbriae and the uterotubal junction. The other tube was ligated at the fimbriae only. The animals were autopsied at 12, 24, 36 or 48 hours after ligation and the luminal fluid in the tubes was aspirated by a microsyringe and measured volumetrically. The rate of accumulation of luminal fluid was highest in the first 24 hours and declined thereafter. When both ends of the tube were ligated, the volume of accumulated fluid within 24 hours varied from 0.71 to 1.37 ml. Maximum output of fluid occurred one to three days after copulation. There was no characteristic change in the fluid volume throughout pregnancy. When the uterotubal junction was not ligated, the luminal fluid accumulated in all stages of pregnancy except at three and four dayspost coitum, then at the time at parturition. The first period coincided with the time when the embryos are transported through the uterotubal junction. Shortly before and shortly after parturition the uterotubal junction relaxed, presumably because of the hormonal environment. This is evidence that a reversal in the flow direction of the luminal fluid may take place during pregnancy. The ligature of the fimbriae had no harmful effect on the cleavage rate of embryos or rate of transport through the uterotubal junction. In the immature animal, the output of luminal fluid was less than the adult and the uterotubal junction is relatively relaxed.