The ascorbic acid and glutathione content, the O2 uptake, and the cyto-chrome oxidase conc. of the uteri of mature rabbits were recorded during estrus and at days 3, 6, 12, 19 and 28 of pregnancy. The ascorbic acid conc. the O2 uptake and oxidase concs. increased 75% at the 3d day of pregnancy, declining somewhat thereafter. The glutathione content increased less markedly and declined to levels below that of estrus. Adrenal and ovarian ascorbic acid and glutathione concs. rose to a maximum on the 3d day, declining thereafter. Pituitary concs. varied irregularly. The uteri of immature [female] rabbits injected with gonadotrophic pituitary hormone showed increased O2 uptake and ascorbic acid conc. on the 3d day after inj. of an ovulating dosage accompanied by mating. The pituitaries of the injected animals uniformly contained higher ascorbic acid concs. than the pituitaries of uninjected controls. The adrenal and ovarian ascorbic acid concs. varied irregularly. Iodoacetate, cyanide and salicyldoxime inhibit the O2 uptake of rabbit endo-metria in vitro. The O2 uptake is not enhanced by the addition of glucose or succinate.