The objects of this investigation are (1) to ascertain the value of quantitative determinations of the diastatic activity1 of urine in revealing renal functional capacity in cardiac, cardiorenal and renal cases ; (2) to compare in the same group of cases the findings of diastase, urea and phthalein in the urine with those of urea, total incoagulable nitrogen and cryoscopy in the blood, and (3) to compare the relative value and limitations of the tests of retention with those of excretion. Renal functional capacity is usually ascertained in one of two ways : (1) Tests of excretory capacity through the quantitative determination of the secretion of various substances in the urine — dyes, methylene blue, indigocarmin, rosanilin and phthalein ; other chemicals, potassium iodid, lactose, salicylates, sodium chlorid, urea, sugar following phloridzin and the enzyme, diastase. (2) Tests of retention through the determination of the concentration of certain substances in