Abstract
A 57-year-old woman presented with symptoms which were cured by the removal of an insulinoma. The case was atypical in that symptomatic hypoglycaemia occurred only after meals or glucose administration but never during fasting, and thus if plasma insulin activity had not been measured an incorrect diagnosis of reactive hypoglycaemia might have been made on the basis of symptoms and oral glucose-tolerance test. Reactive hypoglycaemia resulted from an increased rate of glucose assimilation and possibly also from a decreased rate of gluconeogenesis due to the immense insulin secretion provoked by glucose or food. The findings suggest that a diagnosis of hypoglycaemia should not be made until the possibility of an insulinoma has been excluded by measurement of plasma insulin activity during a period of hypoglycaemia.