Electroencephalographic monitoring of spontaneous interictal spiking (SIS) following kindling demonstrated that SIS occurs in both amygdalas and that it declines sharply during the days following kindling. Systemically administered muscarinic antagonists which pass the blood-brain barrier (atropine and scopolamine) activated interictal spiking in kindled rats but not in controls. Interictal spiking activated by atropine was reversed by physostigmine. Both physostigmine and choline, agents which increase brain ACh concentration by different mechanisms, caused a reduction in spontaneous (not drug activated) interictal spiking. The results of these pharmacologic studies indicate that the interaction of endogenous ACh with central muscarinic receptors is capable of suppressing SIS in kindled rats. Whether cholinergic suppression of SIS represents a convulsant or an anticonvulsant action is presently unclear.