A cartridge (10) for dispensing a reagent contained in a reagent reservoir (32). The reservoir (32) is in fluid communication with a deformable dispense tube (26) that is a least partially compressible, in use, to dispense a volume of reagent from the tube (26). The reservoir (32) defines an enclosed gas space (46) above the reagent, and the cartridge (10) includes a gas vent (40) that, in use, admits gas to the gas space (46) in response to dispense of reagent from the tube (26) that serves to control the reservoir pressure as the reservoir (32) is depleted by subsequent dispensing of reagent. A dispenser employing the cartridge (10) and a method of dispensing a volume of reagent are also disclosed.