The blood-brain barrier was opened by intracarotid infusion of 5 mg protamine sulfate in 100 microliters 0.9% NaCl over a period of 30 s either alone or followed by infusion of 10 mg L-glutamate in 0.9% NaCl. Glutamate alone was infused in four control rats. Cisternal cerebrospinal fluid (CSF) was withdrawn before protamine administration and before the brains were fixed in situ 1, 24 or 72 h later. The albumin extravasation and glial reactivity was evaluated by immunohistochemistry on paraffin sections. The CSF albumin was significantly increased in both the protamine and protamine/glutamate groups but remained high at 24 and 72 h in the protamine/glutamate group only. Spongiotic lesions with shrunken nerve cells were observed 1 and 24 h after infusion of protamine alone or in combination with glutamate. Whereas such changes were not seen 72 h after protamine infusion, they remained and had progressed at 72 h in the protamine/glutamate group, indicating that glutamate induces delayed cellular damage when given access to the brain through an altered blood-brain barrier.