A model of experimental intracerebral hemorrhage is described in which carefully controlled volumes of autologous blood were injected at arterial pressure into the caudate nucleus of the rat. A comparison of intracranial pressure changes and local cerebral blood flow (CBF) was made between three groups of rats, each receiving different injection volumes, and sham-operated control rats by monitoring intraventricular pressure and by obtaining quantitative autoradiographic measurements of CBF within 1 minute of the experimental hemorrhage. Cerebral blood flow was reduced both around the hematoma and in the surrounding brain. This change was strongly volume-dependent and was not accompanied by significant alterations in cerebral perfusion pressure. This finding suggests that the degree of ischemia at the time of an intracerebral bleed depends on the size of the lesion, and implicates local squeezing of the microcirculation by the hematoma, rather than a generalized alteration in perfusion pressure, as the cause of ischemia.