The effects of noradrenaline (NA) and alpha- and beta-adrenergic agonists on neocortical neurons in rat brain slices were studied by intracellular recording. NA added to the perfusion medium decreased the orthodromically evoked excitatory postsynaptic potential (EPSP) and increased the neuronal excitability on current injection. The decrease of the EPSP by NA was mimicked by alpha-adrenoceptor activation. The beta-adrenergic agonist, isoprenaline, increased the neuronal excitability to current injections similarly to NA. In addition, isoprenaline markedly increased the amplitude of a late component of the EPSP (I-EPSP). The increase of the I-EPSP was long-lasting (up to 90 min). Since this late component of the EPSP is blocked by the NMDA (N-methyl-D-aspartate)-antagonist APV (D-2-amino-5-phosphonovalerate), an enhancement of this excitatory synaptic transient via beta-adrenoceptors may be relevant for the facilitatory effect of NA on neuronal plasticity.