Changes in intracellular Caz+ concentration ([Ca*+] J in the soma and dendrites of hippocampal CA1 pyramidal neurons were measured using intracellularly injected fura-2. A large component of the [Ca*+] i elevation caused by high frequency stimulation of the Schaffer collaterals was correlated with the Na+ spikes triggered by the excitatory postsynaptic potentials (EPSPs). These spikes were generated in the soma and proximal dendrites and stimulated Ca*+ entry through voltage-gated Ca*+ channels. Suppressing spikes by hyperpolarizing the soma or by injecting QX-314 revealed a smaller nonspike compo nent of Ca*+ entry. A substantial fraction of this component was mediated by the action of the EPSPs on voltagc-gated Ca*+ channels, because it persisted in 2-amino-5-phosphonovaleric acid and because it was usually reduced when Ca*+ channel activity was sup pressed by hyperpolarization. Ca*+ entry through the N-methyl-o-aspartate receptor channel could not be detected with certainty, perhaps because it was highly localized.