Organic solvents, such as ethanol or dimethyl sulphoxide (DMSO), have been used in liquid embolic agents. To investigate the effects of these solvents on the cerebral blood vessels and cerebral tissue, we subjected Wistar rats weighing 250-300 g to internal carotid artery infusion of 0.2 ml diluted ethanol (10%, 40% or 70%) or anhydrous DMSO (100%). Some rats were sacrificed 5 min after the infusion and the remainder at 10 days. Rats injected with ethanol at high concentration or DMSO showed extensive exudation of Evans blue at the site of injection 5 min after infusion, together with full-thickness necrosis of the wall of vessels and swelling of brain cells. In contrast, rats injected with 10% or 40% ethanol solution showed necrosis of only the intimal layer and partial necrosis of the medial layer and no brain swelling was observed. These findings suggest that ethanol at low concentration can be used as a relatively safe solvent for liquid embolic substances.