After transferring fetuses to the abdominal cavity of the mother in such manner that the umbilical cord passed through a window in the uterine wall and the placenta retained its normal attachment, the outlet of the fetal bladder was blocked by ligating the urogenital papilla. Exactly 2 hrs. after liga-tion, the fetus was secured by severing the umbilical cord (about 16 hrs. before expected parturition). When a highly concentrated soln. of urea was injected under the skin of the fetus, the wt. of urine in the bladder was significantly greater than in controls which received subcut. injns. of water or of normal saline. It would seem that the urea did not act as a specific diuretic agent since there were marked changes in osmosis (subcut. edema). Ligation of the renal pedicles of the mother 24 hrs. before ligation of the urogenital papilla speeded up the rate of secretion of fetal urine. Presumably this was due to the accumulation of metabolites in the maternal circulation.