The effect of long-term oral administration of norethynodrel and 17α-ethynyl oestradiol-3-methyl ether (mestranol, EO3Me) on biochemical changes in the uterus, ovary and adrenal of rabbits has been studied. It was found that the administration of norethynodrel significantly increased the incorporation of [U-14C]glucose into lipid, RNA and protein of the rabbit uterus. In this respect, the effect of norethynodrel resembled that of an oestrogenic compound besides its known progestational action. EO3Me increased glucose metabolism and its incorporation into lipid and RNA in the uterus. Norethynodrel also increased lipid and protein synthesis in the ovary, but EO3Me enhanced only lipid synthesis in the ovary. Glucose metabolism was markedly depressed in the adrenal gland after the administration of norethynodrel. The mode of action of norethynodrel has been discussed in relation to the disturbance in the biochemical changes it produced in the uterus and the ovary.