The common preconception about central nervous system neurones is that thousands of small postsynaptic potentials sum across the entire dendritic tree to generate substantial firing rates, previously observed in in vivo experiments. We present evidence that local inputs confined to a single basal dendrite can profoundly influence the neuronal output of layer V pyramidal neurones in the rat prefrontal cortical slices. In our experiments, brief glutamatergic stimulation delivered in a restricted part of the basilar dendritic tree invariably produced sustained plateau depolarizations of the cell body, accompanied by bursts of action potentials. Because of their small diameters, basolateral dendrites are not routinely accessible for glass electrode measurements, and very little is known about their electrical properties and their role in information processing. Voltage-sensitive dye recordings were used to follow membrane potential transients in distal segments of basal branches during sub- and suprathreshold glutamate and synaptic stimulations. Recordings were obtained simultaneously from multiple dendrites and multiple points along individual dendrites, thus showing in a direct way how regenerative potentials initiate at the postsynaptic site and propagate decrementally toward the cell body. The glutamate-evoked dendritic plateau depolarizations described here are likely to occur in conjunction with strong excitatory drive during so-called 'UP states', previously observed in in vivo recordings from mammalian cortices.