An experimental study was performed to investigate the gastrointestinal motility and in-utero defecation by radio-nuclide techniques. Forty-eight New-Zealand white rabbit fetuses at 25 days' gestation (fullterm, 31 to 32 days) were divided into two groups as A (n: 24) and B (n: 24). 0.1 ml of Technetium-99m ((TC)-T-99m)-HIDA (a derivative of iminodiacetic acid) containing 1 mCi of radioactivity was injected into the gluteus muscle of each fetus, which had been exposed through the uterus. This procedure was used for all fetuses and additionally surgical closure of anus by a purse string suture was performed in Group B fetuses. After replacing the fetus and uterus into the abdomen, and beginning 1 hour after injection, a live fetus was killed each hour for 24 hours. Tissue samples from the reference organs (lung, heart, stomach, kidney, bladder), liver, meconium in the proximal, mid and distal bowel, and amniotic fluid were taken. The radioactivity of each sample was determined by a gamma counter and the percentage injected dose (uptake) per gram of tissue is calculated. Tc-99m-HIDA Was predominantly trapped by the liver via systemic circulation and excreted into the gastrointestinal tract in both groups through which it passed into the amniotic fluid only in Group A. The very low radioactivity levels detected in the amniotic fluid of Group B originated from urinary tract and indicated the in-vivo stability of Tc-99m-HIDA, thus reliability of the experimental model, intestinal-transport of a radiopharmaceutical agent in both groups and demonstrated passage into the amniotic fluid only in Group A strongly suggest that fetal defecation is a physiologic event.