The possibility of intra-uterine treatment of the fetus through the amniotic fluid is emphasized by this study with intra-amniotic injection of glucose, sulfa-drug and corticoid. The findings are summarized: (1) In in vitro experiments, glucose and sulfa-drug practically failed in passing through the fetal membrane, whereas in in vivo, both withdrew from the amniotic fluid almost in parallel. (2) When sulfa-drug was injected into the amniotic fluid, its level elevated transitorily in both the maternal and umbilical vein blood. But its concentration was definitely higher in the latter than in the former within several hours after injection, suggesting that sulfa-drug in the amniotic fluid probably first enters the fetal body, presumably by swallowing, and then passes across the placenta to the maternal blood. Similarly, prednisolone injected in the amniotic fluid was associated with gradual fall in the level of 17-OHCS. (3) In cases with hydramnios, both glucose and sulfa-drug injected in the amniotic fluid showed a very slow withdrawal. (4) These results encourage substantial studies for the establishment of some therapeutic formula via intra-amniotic medication.