A device (200) for mixing first and second substances. The device comprises a first container (100) for storage of the first substance and a second container (150) received in the first container (100) and for storage of the second substance. An outlet (112) is disposed at the distal end of the first container (100). Valve means (180) are provided for closing a distal end of the second container (150) and a proximal end of the first container (100). A stopper means (166) closes a proximal end of the second chamber (152) and is movable with respect to the second container (150). An operating mechanism drives relative movement between the first and second containers for causing displacement of the second substance into the first chamber (102) through the valve means (180) when the outlet (112) is closed, for mixing the first and second substances in a mixing stroke of the device.
