The normal spontaneous bursting behavior of hippocampal pyramidal neurons was investigated. Bursting frequency was found to be membrane potential dependent, the frequency increasing with maintained depolarization and decreasing upon hyperpolarization. Short depolarizing-current pulses would trigger bursts which outlasted the stimulus, and bursting continued when synaptic transmission had been blocked. The spontaneous bursts of these neurons, in contrast to bursts induced by convulsive agents, appear to exhibit the classical behavior of endogenous bursts as observed in invertebrate neurons. The endogenous bursts in hippocampal neurons may result, also, from an interplay of intrinsic membrane currents.