The purpose of this report is to compare the effect of acute therapy with dimethyl sulphoxide (DMSO) and pentobarbitone on experimental brain oedema produced by a cryogenic lesion over the left hemisphere in albino rabbits. A group of animals received DMSO (1 mg/kg-10% solution) by intravenous bolus, and another group received a pentobarbitone intravenous 30-minute infusion (40 mg/kg). Intracranial pressure (ICP), systolic arterial pressure (SAP), central venous pressure (CVP), and EEG were studied. Brain water and electrolyte content were analyzed at one hour following the initiation of therapy. ICP was promptly reduced with both forms of therapy. A 66% reduction from control values was reached at 50 +/- 12 minutes with pentobarbitone, and a 45% reduction from control values was reached at 30 minutes with DMSO. There was no significant reduction in the water content of the brain with either form of therapy. A significant elevation in brain potassium content was noted following DMSO when compared to untreated controls. CVP was essentially unchanged in both groups. Pentobarbitone produced a reduction of SAP with a mean value of 20.3 torr at 45 minutes from infusion. DMSO produced no reduction of SAP. It is concluded that DMSO and pentobarbitone are just as effective in reducing ICP. DMSO has the capacity to maintain SAP which pentobarbitone does not have, thus assuring a better cerebral perfusion pressure.