The toxicity of kainic acid toward rat hippocampal neurons depends on the presence of specific excitatory afferents. Acute destruction of the critical pathway essentially abolishes the neurotoxicity of intraventricular kainic acid, but some or all hippocampal neurons continue to be destroyed by locally-injected kainic acid until the critical pathway(s) degenerates. These results support the view that kainic acid destroys hippocampal neurons in two ways: (1) by initiating a lethal status epilepticus; and (2) by interacting with certain pathways independently of on-going electrical activity within those pathways.