To assess serial changes in blood pressure and its circadian variation following a lacunar stroke, the authors studied 7 patients who developed a single lacunar infarction in either the internal capsule or the corona radiata. Blood pressure and pulse rate were monitored noninvasively for twenty-four hours by an ambulatory blood pressure monitoring device in the acute, subacute, and chronic phases of the strokes. In the acute and chronic phases, the authors also measured urinary excretion of catecholamines every 6 hr, and serum cortisol concentration at 9:00, 17:00, and 21:00 hr. The patients were free from antihypertensive agents during the study. The twenty-four-hour averages of both systolic and diastolic blood pressure in the chronic phase were lower than those in the acute phase (P < 0.05). A nighttime fall in blood pressure was observed in the subacute and chronic phases (P < 0.05), but not in the acute phase. Urinary excretion of epinephrine at night in the acute phase was significantly higher than that in the chronic phase (P < 0.05). Serum levels of cortisol at 17:00 and 21:00 hr in the acute phase also exceeded those in the chronic phase (P < 0.05 and P < 0.01, respectively). The authors conclude that an increased secretion of epinephrine and cortisol might, at least in part, contribute to a high blood pressure and a lack of circadian variation in blood pressure in the acute phase of lacunar stroke.