1.1. The human female, in health, has a series of definite assimilation limits for galactose, the fluctuations of which are seemingly associated with changes of physiologic activity of ovarian function.2.2. Starting at a low level in prepubertal years, with the onset of puberty the tolerance rises to a level in maturity double the first, and maintains this until the cessation of the catamenia is accompanied by a recession of moderate degree.3.3. To those whose level is superior to the prepubertal, the act of menstruation usually determines a slight depression in the tolerance.4.4. Castration of the adult lowers the sugar tolerance to the prepubertal level, and functional failure exhibits the same tendency, the degree of the depression correlating with the severity of the impairment.5.5. The mammary glands are shown to have an important but apparently secondary influence in determining assimilation limits.6.6. The menstrual relationships consititute a possible exception, but presumably are more closely associated with the events of the reproductive cycle, which are not considered in this paper.7.7. In the main, the results of the study are in harmony with Frank's observations and his theory of the female sex hormone. Equally, the results could be explained by other endocrine formulas wholly independent of the foregoing.8.8. The interstitial glands, at least during adult years, seemingly have only a secondary influence, if any, on the regulation of galactose tolerance.9.9. The reproductive phase is to be considered independently in a subsequent paper.