Abstract: A sump for an anaesthetic vaporiser comprises a vaporising chamber for liquid anaesthetic agent, a heater for liquid anaesthetic agent contained within the chamber, and a partition member of which at least a portion extends into the chamber to entrap a portion of liquid anaesthetic agent at a location in close proximity to the heater, the member having a partition outlet for anaesthetic agent vapor through the partition member at a position above the maximum level of anaesthetic agent within the partition member. The partition member allows a portion only of liquid anaesthetic agent within the vaporizing chamber to be heated, so that the temperature required of the liquid agent for operation of the vaporiser can be reached rapidly. The sump finds particular application in connection with the use of low boiling point anaesthetic agents such as 2 -(difluoromethoxy) 1,1,1,2 -tetrafluoroethane.