This study examines the effects of ovarian hormones on the glycaemic actions of insulin, glucagon and epinephrine. Ovariectomized adult female mice were treated with replacement doses of oestradiol, progesterone, both hormones combined or vehicle only for 15 weeks. Compared with intact control mice, ovariectomy did not significantly alter insulin-induced hypoglycaemia. However, treatment with oestradiol or progesterone alone, but not in combination, increased the hypoglycaemic action of insulin. The hyperglycaemic effect of glucagon and epinephrine was increased by ovariectomy and reduced by the ovarian hormone treatments. The results indicate that oestradiol and progesterone individually synergize the hypoglycaemic action of insulin, but mutually antagonize each other in this respect. Oestradiol and progesterone, individually and in combination, appear to suppress the glycogenolytic action of glucagon and epinephrine.