The effect of in vivo corticosterone manipulation on binding sites for the excitatory neurotransmitter glutamate was determined using radioligand binding to rat brain cryostat sections and crude synaptic membranes. 3H-glutamate binding to regions of the dorsal hippocampal formation was significantly decreased in adrenalectomized animals following 5–10 days of corticosterone treatment. Corticosterone did not alter 3H-glutamate binding in several other brain regions. The loss in 3H-glutamate binding appeared to be due to a decrease in the maximal number of binding sites, with little change in binding affinity. Both chloride-dependent and chloride-independent 3H-glutamate binding sites were decreased by corticosterone treatment. Results indicate that corticosterone can selectively alter binding sites for excitatory amino acids in hippocampal tissu