Two critically ill patients are described in whom the intravenous administration of Dilantin produced marked alterations in plasma glucose and blood pressure. The first patient, a nondiabetic with chronic lung disease received a total of 1.8 gm. Dilantin over a 48-hr, period for status epilepticus. Plasma glucose increased from normal to 1,200 mg./100 ml. and his seizures became focal in nature. The second patient, a mildly diabetic male, experienced renal shut-down and multiple arrythmias after a myocardial infarct. Three hours after a single intravenous injection of 200 mg. Dilantin, plasma glucose rose from 400 mg. to 1,260 mg./100 ml. and proved relatively resistant to insulin. Intravenous administration of 25 mg. Dilantin per kg. in four dogs promptly induced marked hyperglycemia and hypotension.