A medicament delivery device comprising: a housing; and a syringe axially movable in the housing, the syringe having a barrel; characterised in that the device further comprises: a stopper axially movable in the barrel, the stopper separating a first chamber and a second chamber from one another, the first chamber being axially forward of the stopper and configured to receive a medicament and the second chamber being axially rearward of the stopper and configured to receive a propellant from a propellant source to provide a vapour pressure to the second chamber, the stopper being axially movable in the barrel between a first stopper position and a second stopper position in response to the vapour pressure being received in the second chamber; and a biasing mechanism configured to axially move the syringe in the housing between a first syringe position and a second syringe position in response to a first reduction in the vapour pressure in the second chamber, wherein in the first syringe position venting of the propellant from the second chamber through a first fluid pathway is permitted to enable the first reduction in the vapour pressure in the second chamber while venting of the propellant from the second chamber through a second fluid pathway is substantially prevented, and wherein in the second syringe position venting of the propellant from the second chamber through the second fluid pathway is permitted to enable a second reduction in the vapour pressure in the second chamber. a housing; and a syringe axially movable in the housing, the syringe having a barrel; characterised in that the device further comprises: a stopper axially movable in the barrel, the stopper separating a first chamber and a second chamber from one another, the first chamber being axially forward of the stopper and configured to receive a medicament and the second chamber being axially rearward of the stopper and configured to receive a propellant from a propellant source to provide a vapour pressure to the second chamber, the stopper being axially movable in the barrel between a first stopper position and a second stopper position in response to the vapour pressure being received in the second chamber; and a biasing mechanism configured to axially move the syringe in the housing between a first syringe position and a second syringe position in response to a first reduction in the vapour pressure in the second chamber, wherein in the first syringe position venting of the propellant from the second chamber through a first fluid pathway is permitted to enable the first reduction in the vapour pressure in the second chamber while venting of the propellant from the second chamber through a second fluid pathway is substantially prevented, and wherein in the second syringe position venting of the propellant from the second chamber through the second fluid pathway is permitted to enable a second reduction in the vapour pressure in the second chamber. a stopper axially movable in the barrel, the stopper separating a first chamber and a second chamber from one another, the first chamber being axially forward of the stopper and configured to receive a medicament and the second chamber being axially rearward of the stopper and configured to receive a propellant from a propellant source to provide a vapour pressure to the second chamber, the stopper being axially movable in the barrel between a first stopper position and a second stopper position in response to the vapour pressure being received in the second chamber; and a biasing mechanism configured to axially move the syringe in the housing between a first syringe position and a second syringe position in response to a first reduction in the vapour pressure in the second chamber, wherein in the first syringe position venting of the propellant from the second chamber through a first fluid pathway is permitted to enable the first reduction in the vapour pressure in the second chamber while venting of the propellant from the second chamber through a second fluid pathway is substantially prevented, and wherein in the second syringe position venting of the propellant from the second chamber through the second fluid pathway is permitted to enable a second reduction in the vapour pressure in the second chamber.