An automatic injector is provided having at least two chambers containing different ingredients of a medicament separated by .�.an impermeable membrane. A lance is movable independently of a plunger to cut or pierce the membrane before a spring-loaded drive member for the plunger is released to drive a needle out of the body of the injector and discharge the medicament through the needle. A removable safety clip is provided for preventing movement of art actuating cap into an operative position for advancing the lance, and release of the drive member is preventable by a removable safety pin until the injector is to be used..!. .Iadd.a sealing structure. One of the chambers has a needle disposed therein. The sealing structure is conditionable to permit the ingredients to mix in the injector in response to a predetermined actuating procedure before the ingredients are injected.