Puberty in the girl was shown in a previous communication1 to be associated with a fall in the retention of calcium and nitrogen, a fact which might be anticipated if one recalls the prompt diminution in the rate of growth associated with the attainment of sexual maturity. The phenomena of a rapid increase in the rate of growth preceding puberty and the fall following it have been shown to correlate with physiologic and not with chronologic age. It has likewise been shown that there is a rise in the basal metabolic rate associated with the increasing rate of growth and the increasing retention of calcium and nitrogen and a fall in the metabolic rate coincident with the diminishing retention of these two substances; in other words, changes in the metabolic rate paralleled directly, rather than inversely, the retentions of calcium and nitrogen, though an inverse relation might have been expected from the result of work on the effects of thyroid on adults. The present inquiry was planned to study the effect of estrogenic substance on the retention of these substances in the girl at puberty.Katzman and Doisy2 have demonstrated that there is a cyclic excretion of estrogenic substance even before the onset of menstruation, and in the blood of the normally menstruating woman Frank3 has described a gradual increase in the excretion of this substance in the week just preceding the onset of the flow and a sharp disappearance two to six hours after the onset of the flow.