1. The effects of anaesthetics (pentobarbitone, hexobarbitone, halothane, urethane, chloralose, chloral hydrate and ethanol) on the extracellular field potentials of the olfactory bulb produced by lateral olfactory tract stimulation were analysed.2. Relatively large doses of all the anaesthetics (e.g. pentobarbitone, 40-70 mg/kg) depressed the synaptic excitation of granule cells.3. The antidromic invasion of mitral cell dendrites was only slightly less sensitive to the anaesthetics than was the synaptic excitation of granule cells.4. A wide dose range of anaesthetics (e.g. pentobarbitone, 3-60 mg/kg) prolonged the granule cell post-synaptic inhibition of mitral cells. All the anaesthetics, except ethanol, prolonged the inhibition.5. The action of anaesthetics on post-synaptic inhibition was due to a specific effect on the inhibitory synapses.6. Amino-oxyacetic acid, an inhibitor of GABA catabolism, had little effect on the synaptic inhibition or on the ability of hexobarbital to prolong the inhibition. This suggests that the prolongation seen with anaesthetics is not a result of interfering with GABA catabolism.7. The present results are compared with results obtained with anaesthetics in other areas of the nervous system and it is proposed that prolongation of ;gaba-ergic' inhibition might contribute to an agent's ability to produce general anaesthesia.