The electrophysilogical effects of luteinizing hormone-releasing hormone (LHRH) on CA1 pyramidal cells were investigated utilizing intracellular recodings from the in vitro rat hippocampal slce preparation. Bath application of LHRH (10-7-10-12M) resulted in several changes in the electrophysiological properties of CA1 neurons. LHRH induced a long-lasting depolarization associated with increased input resitance, and decrease in the afterhyperpolarization associated with increased input resistance, ad decrease in the afterhyperpolarization (AHP) following a train of action potentials, and a reduction in accommodation of repetitive cell discharge. These effects were blocked by the synthetic LHRH antagonist [Ac-δ-Pro1, pCl-D-Phe2, D-Trp3,6]-LHRH. These findings provide electrophysiological evidence for the role of LHRH as a neurotransmitter/neuromodulator in the hippocampus.