The invention relates to a method and a device for lyophilizing, reconstituting and administering a reconstituted substance. The device has an elongate housing having a dispensing-side front housing end and a housing end lying opposite it. A first chamber, containing a lyophilizate, is disposed in the housing in the region of the front housing end and is tightly sealed at an end facing the front housing end by a removable closure and is tightly sealed in the direction of the rear housing end by a plunger. A second chamber is provided or formed in the housing in the region of the rear housing end which is connected by at least one opening to the ambient atmosphere. This opening is closed by a membrane which is permeable to gas but not to bacteria.