The accumulation of calcium in the hippocampal and thalamic vascular endothelium and the perivascular space was detected histochemically by means of the pyroantimonate technique 30, 60 and 120 min after systemic kainic acid administration. An increased number of calcium pyroantimonate deposits was found in the endothelial mitochondria 60 min after kainate injection. The mitochondria were swollen at this time and vacuoles containing deposits were observed. After 120 min a pronounced perivascular glial swelling was conspicuous, besides the numerous endothelial mitochondrial deposits. The swollen glial processes contained a large number of pyroantimonate deposits. It seems likely that the transendothelial calcium transport processes are accompanied by intraendothelial calcium accumulation and mitochondrial calcium sequestration.