An automatic injection device for containing a pre-loaded charge of medicament for automatically administering the medicament upon actuation thereof, the device comprising: a housing having an interior chamber, the interior chamber including a dry compartment for containing a dry medicament component, and a wet compartment for containing a liquid component to be mixed with a said dry component; a seal structure between the dry compartment and the wet compartment, the seal structure being initially in a sealing condition that maintains the dry compartment sealed from the liquid compartment; a needle assembly for dispensing a charge of medicament from the housing; a plunger disposed within the chamber and movable through the chamber to force the charge of medicament through the needle assembly; and an activation assembly received within the housing and including a stored energy source, wherein activation of the activation assembly releases the stored energy from the stored energy source; characterized in that: the seal structure comprises an outer seal member, a flow path, an inner seal plug movable with respect to the outer seal member, and a filter or membrane that creates a laminar fluid flow as the liquid component passes through the seal structure from the wet compartment to the dry compartment; the inner seal plug sealing the wet compartment from the dry compartment in the sealing condition and allowing the contents of the wet and dry compartments (151,152) to mix when moved into a mixing position; and in that: the release of the stored energy by the activation assembly causes: the inner seal plug to move to the mixing position, which converts the seal structure from the sealing condition to a mixing condition that permits a said liquid component to pass through the flow path from the wet compartment to the dry compartment; a said liquid component to be forced through the filter or membrane to the dry compartment for mixing with a said dry medicament component; and, said mixed liquid and dry components to be forced through the needle assembly. a housing having an interior chamber, the interior chamber including a dry compartment for containing a dry medicament component, and a wet compartment for containing a liquid component to be mixed with a said dry component; a seal structure between the dry compartment and the wet compartment, the seal structure being initially in a sealing condition that maintains the dry compartment sealed from the liquid compartment; a needle assembly for dispensing a charge of medicament from the housing; a plunger disposed within the chamber and movable through the chamber to force the charge of medicament through the needle assembly; and an activation assembly received within the housing and including a stored energy source, wherein activation of the activation assembly releases the stored energy from the stored energy source; the seal structure comprises an outer seal member, a flow path, an inner seal plug movable with respect to the outer seal member, and a filter or membrane that creates a laminar fluid flow as the liquid component passes through the seal structure from the wet compartment to the dry compartment; the inner seal plug sealing the wet compartment from the dry compartment in the sealing condition and allowing the contents of the wet and dry compartments (151,152) to mix when moved into a mixing position; and in that: the inner seal plug to move to the mixing position, which converts the seal structure from the sealing condition to a mixing condition that permits a said liquid component to pass through the flow path from the wet compartment to the dry compartment; a said liquid component to be forced through the filter or membrane to the dry compartment for mixing with a said dry medicament component; and, said mixed liquid and dry components to be forced through the needle assembly. a said liquid component to be forced through the filter or membrane to the dry compartment for mixing with a said dry medicament component; and, said mixed liquid and dry components to be forced through the needle assembly.