Blood glucose was determined during or immediately after a fit in 39 children with 'febrile convulsions' and in 6 with other fits. In 22 of the 39 children blood glucose over 120 mg/100 ml was found. In 6 children the levels exceeded 200 mg/100 ml. 2 hours after the seizures the blood glucose levels returned to normal. It is important to recognize this phenomenon to prevent an incorrect diagnosis of diabetes mellitus and inappropriate treatment with insulin.