Abstract: A medical injector system includes a hypodermic ampule having a body, a piston sealingly forwardly movable therein for defining a medicament chamber, a pierceable seal closing a front extremity of the ampule, a needle movably axially supported by the piston and biased rearwardly toward a retracted, cocked position. An actuator removably receives the ampule, and has a spring-loaded plunger for advancing the needle, and then the piston, whereby the needle reaches an extended position, medicament being injected from the needle during the forward movement of the piston. When the plunger is released, it retracts from the needle and the piston, the needle automatically retracting into the ampule for preventing accidental injury and contamination that might otherwise result from having the used needle in an exposed position.