A container (2) for a liquid anaesthetic agent for supplying the agent to an anaesthetic vaporiser comprises a reservoir for the liquid agent, a valve (6) which, when closed, prevents the flow of the liquid agent from the reservoir, a tubular outlet (10) through which the liquid can leave the reservoir when the valve is open. An O-ring (20) at the free end of the conduit provides a sealing surface for forming a seal with a corresponding sealing surface provided at an inlet to a vaporiser to which the anaesthetic agent is to be supplied. A flange (22) engages a guide on the vaporiser, to retain the container in contact with the vaporiser.