&NA;&bgr;‐Adrenergic agents are used to inhibit preterm labor and glucocorticoids to accelerate fetal pulmonary maturation. A study was designed to investigate the metabolic effects of intravenous infusion of ritodrine (150 to 100μg/min) or isoxsuprine (200 to 150μg/min) in a series of 28 patients with gestations of 28 to 40 weeks, with and without concomitant dexamethasone therapy. Ritodrine was more potent than isoxsuprine in increasing the circulating levels of cyclic AMP, glucose, insulin, and triglycerides. The diabetogenic effect of both ritodrine and isoxsuprine was so slight that it did not have any clinical significance in women with normal glucose tolerance. The results were similar when these &bgr;‐adrenergic tocolytics were given to women concomitantly with intramuscular dexamethasone therapy, although dexamethasone appeared to minimally impair carbohydrate metabolism. Both ritodrine and isoxsuprine caused a significant fall in serum iron and potassium, and this effect was unaltered by dexamethasone. Serial serum potassium levels should be obtained during long‐term infusion of &bgr;‐mimetics.