An injection device (10； 110, 210) is described. A housing (12； 112, 212) receives a syringe and includes a return spring (26； 126, 226) for biasing the syringe from an extended position in which its needle (18； 118, 218) extends from the housing to a retracted position in which the it does not. A drive spring (30； 130, 230) acts on a first drive elements (32； 132, 232) and a second drive element (34； 134, 234) acts upon the syringe to advance it from its retracted position to its extended position and discharge its contents through the needle. The first drive element is capable of movement relative to the second when the former is acted upon by the drive spring and the latter is restrained by the syringe (14, 114, 214). A reservoir (48； 148, 248) is defined between the first drive element and the second drive element, the volume of the reservoir tending to decrease as the first drive element moves relative to the second when acted upon by the drive spring. The reservoir contains a highly viscous fluid and has a vent (44； 144, 244) through which the fluid escapes as the volume of the reservoir (48； 148, 248). The first drive element includes a stem (40, 140, 240) and defines the vent and a collection chamber for fluid and the second drive element includes a blind bore (46； 146, 246) that is open at one end to receive the stem and closed at the other, the bore and the stem thus defining the fluid reservoir. A release mechanism (52； 133, 233) is activated when the first drive element has been advanced to a nominal release position, to release the syringe from the action of the drive spring, whereupon the return spring restores the syringe to its retracted position.
