Initial and follow-up fasting serum glucose levels following acute stroke were evaluated retrospectively in 392 selected hospitalized patients. Transitory reactive hyperglycaemia was observed in a large number of patients (28% of the total series) without a history of diabetes prior to the acute cerebrovascular event. The data from this group suggest a possible relationship between the impairment of carbohydrate metabolism and the type and location of stroke since both the frequency and severity of the hyperglycaemic response were higher in patients with haemorrhagic stroke and brainstem infarction as compared with cerebral infarction. The incidence and degree of the reactive hyperglycaemia were also related to the severity of the acute stroke. There were more comatose patients in the group showing this phenomenon. Initial serum glucose levels in the latter group were higher in unconscious patients than in alert ones. In addition, hospital mortality was significantly higher in these patients. Transitory reactive increases of serum glucose levels were also observed in the majority of patients with a history of overt diabetes prior to the acute stroke. The hyperglycaemic reaction following acute stroke may be attributed to several underlying mechanisms. These include: a non-specific reaction to acute stress and tissue injury with the associated autonomic, hormonal and metabolic alterations; uncovering of underlying latent diabetes by the acute stroke; increased secretion of growth hormone due to stroke-induced hypothalamic dysfunction; and irritation of the glucose regulatory centres in the hypothalamus and brain stem by blood-laden cerebrospinal fluid or local ischaemia.