In the hippocampus, pyramidal cells (PCs) are not the only cell type sensitive to cholinergic stimulation. Two non-pyramidal cell types from animals as young as 8 days demonstrated clear, direct responses to application of cholinergic agonists. These cholinergic actions are excitatory, mostly blocked by muscarinic antagonists, and persist under conditions which block synaptic transmission (TTX, low Ca2+/high Mg2+). Cholinergic agonists may affect different conductances in interneurons than in PCs, sometimes resulting in rapid depolarization. Demonstration of direct excitatory cholinergic effects on inhibitory interneurons supports the view that cholinergically-evoked hyperpolarizations in PCs are due to local circuit interactions.