NITROUS OXIDE anaesthesia invades the middle-ear cavity, resulting in a positive pressure within this cavity. It has been suggested that the pressure may be sufficient to force open the Eustachian tube and evacuate fluid from the middle ear. This study examined the possible influence of nitrous oxide on middle-ear fluid. Pre- and intra-operative tympanograms were obtained on 39 children scheduled for myringotomy surgery. Fluid was found in 83-1 per cent of the operated ears while the absence of fluid was noted in 16-9 per cent. It is possible that the nitrous oxide anaesthetic did cause an evacuation of fluid from this latter group of ears prior to actual surgery.