Part I. Comparative evaluation of the extracting method of antidiuretic hormone from human urine, dan purification of commercial posterior pituitary hormone and extracted urinary antidiuretic substance by means of paper electrophoresis.In order to clarlify the role of the posterior pituitary antidiuretic hormone for the accumulation or conservation of fluid in the body under various clinical conditions, the auther reexamined previously reported extracting methods of antidiuretic substance from urine and chiefly compared the method by Noble & Rindernechit with that of Grollman & Woods with regard to the reliability and recovery.Next investigative approach was to purify the extracted substance from urine by the Noble & Rindernechit's method for a comparison of commercial posterior pituitary antidiuretic hormones by means of paper electrophoresis, and to determine whether the purified material was of posterior pituitary origin.Tne results are concluded as follows : 1) Absorptive method of Noble & Rindernechit, employing zinc ferrocianide, gave constant and satisfactory recovery in extracting antidiuretic hormone from urine, that is, average recovery rate of 85.6% for concentration of antidituretic hormone (Pitressin) I mu./cc to 0.1mu./cc, 68% for concentration of 20μu, /cc to 2μu./cc of urine.On the other hand absorptive method of Grollman & Woods employing active charcoal gave unstable and poor recovery.2) Urinary extracts by adsorption on zinc ferrocianide, on active charcoal, and commercial posterior pituitary hormones can be satisfactorily purified by means of paper electrophoresis under constant voltage of 400V/25cm. in 1.15N acetic acid solution.3) Under the same condition Pituitan (commercial posterior pitutary hormone) can be separated into 8 fractions, extract employing zinc ferrocianide in 7 fractions, active charcoal 10-11 fractions.4) Fraction which has antidiuretic and pressor activity in commercial posterior pituitary hormones and urinary extracts has the same migration distance as the 6th fraction in Pituitan from anode under the above described condition.5) Antidiuretic activity of the fraction markedly increases in the urine of normal subjects after the administration of hypertonic saline solution, and also in diabetes insipidus patients' urine after the administration of the posterior pituitary antidiuretic hormones.