Destruction of the hippocampal perforant path fibers reduced the binding of [3H]GABA to membranes prepared from the rat fascia dentata. This result could be detected 1--4 months after surgery, but not in 10 days or less. Such a delayed response appears most compatible with a transsynaptic effect on GABA receptors. Values of low affinity KD and Bmax decreased by about 65%, but no changes were detected in high affinity binding, Hill slope or pharmacological specificity. These findings are consistent with a desensitization of postsynaptic low affinity GABA receptors, possible caused by excessive release of GABA.