1. Twenty-four hour ambulatory blood pressure monitoring (ABPM) was used to evaluate the blood pressure (BP) changes in acute stroke. 2. Stroke was categorized according to the probable underlying vascular mechanism into lacunar infarction (L), thrombotic infarction (T) and intracerebral haemorrhage (ICH), A total of 37 stroke patients were studied (T = 21, L = 9, ICH = 7). Control patients (n = 15) were acute medical admissions not severely ill or in significant pain. ABPM was performed on day 1 and day 7 following admission. 3. Day 1 mean +/- s.d. 24 h systolic BP (SEP) were L (159 +/- 15.8), ICH (151 +/- 33.4), T (147 +/- 15.2) and controls (134 +/- 17.8). Day 7 mean 24 h SEP were L (138 +/- 9.8), ICH (143 +/- 26.9), T (138 +/- 19) and controls (134 +/- 14.8), In each stroke group BP feb to levels similar to control on day 7, while control mean SEP remained unchanged between days 1 and 7. The highest day 1 BP and the greatest subsequent fall on day 7 occurred for lacunar infarction. Diastolic BP showed similar changes to SEP. 4. The acute stress of hospitalization does not appear to explain elevated BP in acute stroke. Lacunar infarction appears to be particularly associated with temporary BP elevation.