The extent of edema related to infarction assessed by computed tomography was compared with the CSF-lactate concentration in patients with middle cerebral artery (MCA) infarction on the first, third and seventh day following the stroke. A linear correlation between the extent of infarction edema and CSF-lactate level was most distinct on the third day. CSF-lactate concentration on the third day can be considered as a measure of the extent of the accompanying edema which in our study reached its maximum at this time in comparison to the first and seventh day.