For the past several years we have employed a procedure for concentrating the gonadotropic substance in the urine of pregnant women which has yielded an excellent extract for general physiological purposes. The method is not difficult to carry out, is quantitative and the product is non-toxic even though administered in massive doses. The procedure is based on the fact that the gonadotropic material from pregnancy urine is precipitated by tannic acid, and by treating the tannic precipitate with pyridine the active principle is again set free from the tannic acid and becomes water soluble. An aqueous concentrate of tannic acid is added to the urine until no further precipitation takes place and, after standing in the cold for several hours, the precipitate is collected by suction filtration, washed with acetone and powdered. The powder may be stored as such and has been kept for as long as 3 years without detectable loss in activity. For further purification, the powder is extracted 8 to 10 hours with constant stirring with 50% aqueous pyridine (200 cc. per 10 gm.—the equivalent of about 5 liters of the original urine). The residue is removed by centrifuging and re-extracted with a like amount of pyridine solution for the same length of time. The two solutions are united and evaporated in a warm current of air (40°C.) or precipitated by pouring into 10 volumes of acetone, adding a small amount of saturated sodium chloride or sodium acetate solution. The residue is then extracted 4 hours with from 10 to 15 cc. distilled water 5 different times, centrifuging each time (cooling the solution to freezing just before centrifuging aids in throwing down the precipitate). All of the solutions are united and the activity precipitated by adding 10 volumes of acetone. The precipitate, which contains the activity, is removed by centrifuging and again extracted 5 times with from 3 to 5 cc. of water each time and again precipitated with 10 volumes of acetone.