It is well known that the upper urinary tract, especially on the right side, of pregnant women is dilated. Twenty-nine pregnant women showing no abnormalities in urinary examina tions and in obstetrical conditions were selected. A total of 42 examinations were made : 4 at the 5th, 6 at the 6th, 8 at the 7th, 5 at the 8th, 7 at the 9th, 8 at the 10th months of pregnancy and 4 postpartum.In each examination the upper urinary tracts were visualized by means of excretory urography which was performed 10 minutes after intravenous injection of 30 ml of 76% Urografin with precaution to avoid compression of the abdomen.The period during which the examinations were made was divided into two periods: the former period including the 5th, 6th and 7th months of pregnancy, and the latter period including the 8th, 9th and 10th months. RESULTSThe results obtained will be epitomized as follows:1) The position of the right renal pelvis compared with that of the left renal pelvis is shown in Table I. In 4 out of 18 cases the right renal pelvis showed its 311