An injection device (110) comprises a housing (112) adapted to receive a syringe (122) having a discharge nozzle (118), an actuator (114) and a drive (120) acted upon by the actuator which acts upon the syringe to advance it from a retracted position in which the discharge nozzle is contained within the housing to an extended position in which the discharge nozzle extends from the housing. There is a locking mechanism (HS) in communication with the actuator and activatable to be moved from a locked position in which the actuator is prevented from releasing the drive to an unlocked position in which the actuator is operable to act upon the drive to advance the syringe. The locking mechanism or the housing includes integrally formed biasing means (210) adapted to return the locking mechanism to a locked position when it is not activated. There is no need for separate springs to be used to bias the releasable locking mechanism out of the housing.