Glucose, insulin, and cortisol were measured in the blood of rhesus monkeys under several conditions. Glucose and insulin concentrations were higher and cortisol lower shortly after the morning meal than after an overnight fast. Ketamine had no detectable effect on basal (fasting) glucose or insulin values in normal monkeys, even when sedation was maintained for more than 2 h. Ketamine did not appear to affect the response to a glucose load or to insulininduced hypoglycemia. It is concluded that ketamine is a useful agent for pharmacological restraint of rhesus monkeys during studies of glucoregulation.