The effect of TCE on the intraocular pressure was investigated in eight patients under thiopentone nitrous oxide/oxygen anaesthesia, using a muscle relaxant (pancuronium bromide). Pulmonary ventilation was controlled and the end-tidal carbon dioxide was maintained at 5 per cent. In every patient the intraocular pressure was observed to rise as TCE was administered and then to return to the initial level when the administration of TCE ceased.