Glycine-activated single-channel currents in rat central neurones were recorded using the outside-out mode of the patch-clamp technique. The unitary conductance of the current was 21 pS. The current evoked by 10 microM glycine had a mean burst duration of 47.8 (2.6) ms and open probability of 0.09 (0.016). Halothane (1 mM) increased the open probability to 0.19 (0.03) without changing either unitary conductance or burst duration. These results suggest that halothane increased the open probability via an increase in the affinity of the receptor for the agonist. Potentiation of the glycine response may reduce excitability of postsynaptic neurones and may contribute to general anaesthesia produced by volatile agents.