An automatic medicament injector has a first compartment for a first medicament component and a second compartment for a second medicament component. The two compartments are separated by a seal structure that converts from a sealing condition to a mixing condition when the device is activated. The seal structure has a plug that opens a flow path through the seal structure to allow the second medicament component to mix with the first medicament component in the first compartment when the seal structure is in the mixing condition.
