The effects of norepinephrine (NE) and the alpha-1 agonist phenylephrine (PE) on synaptically evoked responses of electrophysiologically identified pyramidal neurons in layer V of rat somatosensory cortex were studied in brain slices using intracellular recording techniques. When added to the bathing medium NE (10 microM) tended to increase the synaptic responsiveness of regular spiking neurons and decrease the responsiveness of intrinsic burst neurons. NE had mixed effects on layer V cells which were characterized as intermediate types between regular spiking and intrinsic burst neurons. PE exerted a similar spectrum of actions on layer V cortical neurons. For both adrenergic agents the greatest facilitating effect was observed on responses to low intensity synaptic stimulation. These results suggest that NE exerts different modulatory actions on different electrophysiologically-defined classes of layer V sensory cortical neurons.