GABA(A) receptor mediated signalling can be divided into fast synaptic (phasic) transmission and tonic GABA(A) receptor signalling in which extrasynaptic receptors are activated by ambient, extracellular GABA. Since extracellular GABA concentrations can change in both health and disease, then tonic GABA currents are variable, responding and contributing to different brain states. The functional role of tonic currents is still unclear. We have recently found that tonic GABA(A) receptor currents in pyramidal cells are outwardly rectifying. This has an important effect on the function of tonic inhibition. In contrast to studies in the cerebellum, hippocampal tonic currents alter the offset rather than the gain of pyramidal cell input-output functions. The magnitude of tonic inhibition depends not only upon the concentration of extracellular GABA but also on the expression of extrasynaptic receptors. We have demonstrated that the receptors mediating tonic currents show adaptive plasticity in epilepsy. This may compensate for increased network excitability at the expense of cognitive function. Thus tonic GABA(A) receptor mediated currents in the hippocampus show adaptive plasticity and play an integral role in regulating neuronal and network excitability.