In the guinea-pig hippocampal CA3 region, the synaptic connection from pyramidal neurons to stratum pyramidale inhibitory neurons is remarkable. Anatomically, the connection usually consists of a single release site on an interneuronal dendrite, sometimes 200 microns or more from the soma. Nevertheless, the connection is physiologically powerful, in that a single presynaptic action potential can evoke, with probability 0.1 to 0.6, a postsynaptic action potential with latency 2 to 6 ms. We construct a model interneuron and show that the anatomical and physiological observations can be reconciled if the interneuron dendrites are electrically excitable. Excitable dendrites could also account for depolarization-induced amplification of the pyramidal cell-interneuron EPSP in the voltage range subthreshold for spike generation.