A hypodermic injection system particularly for use in mass immunizations having a handpiece with a grasping mechanism for holding ampules filled with injectate, a plunger for driving into the ampule to discharge the injectate in an injection process, an injection spring mechanism for driving the plunger, a motor and/or manual mechanism for cocking the injection spring mechanism, and an ampule ejection mechanism for ejecting ampules after use under control of a release mechanism. Ampules can be loaded, used and ejected without contact by the user of the system or the patient being injected. Also disclosed are a filling station for filling ampules through their injection orifices, and an arming device for setting the injection spring. Ampules are disclosed having a piston which is drivable towards an orifice to discharge injectate through the orifice. Ampules are also disclosed having enlarged proximal portions for easy grasping by the grasping mechanism of the injector. Ampules are further disclosed with separators for mixing lyophilized medication and a diluent. Further disclosed are magazines for holding ampules for sequential use by the hypodermic injector. The disclosed system finds particular use as a mass immunization kit for making numerous injections in the field.