SummaryMarked hyperglycaemia and hyperinsulinaemia were observed in two normal women in premature labour treated with an intravenous infusion of a β‐sympathomimetic drug and intramuscular dexamethasone injections. Similar therapy in a chemical diabetic patient caused diabetic ketoacidosis, while treatment of an insulin dependent diabetic with dexamethasone alone resulted in a major increase in her insulin requirements. It is suggested that the diabetogenic effects of β‐sympathomimetic drugs and dexamethasone may be additive and that regular plasma glucose estimations should be made when they are used, especially in patients with impaired glucose tolerance.