Mongolian gerbils were observed for the effects of beta-methasone on ischemic brain edema which developed during ischemia or after blood flow restoration. The severity of brain edema was determined by measuring water content of the ischemic cerebral hemisphere, using the wet and dry methods. Sodium and potassium ions were extracted from homogenized brains with 0.75N HNO2 and ion concentration measured by flame photometry. Passage of RISA from blood into the cerebral parenchyma, as an indicator of blood-brain barrier change, was determined with a gamma-scintillation counter. In the cytotoxic edema model, animals were killed after 9 h permanent ischemia or 3 h after 1 h ischemia. In the simultaneous cytotoxic and vasogenic edema model, the animals were killed either 20 h or 3 days following 1 h ischemia, or 3 h after blood flow restoration following 6 h ischemia. Steroid treatment was ineffective in ischemic brain edema of the cytotoxic or vasogenic type.