We investigated the effects of repeated early-life seizures induced by flurothyl inhalation on intrinsic membrane properties of hippocampal pyramidal neurons from young rats (postnatal day 15-20). Intracellular recordings of CA1 and CA3 pyramidal neurons from flurothyl-treated and control rats revealed no significant differences in resting membrane potential, input resistance, membrane time constant, and action potential characteristics. In CA1 pyramidal cells from flurothyl-treated rats, the spike frequency adaptation and afterhyperpolarizing potential following a spike train were markedly reduced when compared with controls. In contrast, no significant alterations in the firing properties of CA3 pyramidal neurons were found. It is concluded that neonatal seizures lead to persistent changes in intrinsic membrane properties of CA1 pyramidal neurons. These alterations are consistent with an increase in neuronal excitability and may contribute to the behavioral deficit and epileptogenic predisposition observed in rats that experienced repeated neonatal seizures.