A disposable hypodermic syringe having a needle fixed to a piston assembly. The piston assembly is held within the barrel of said hypodermic syringe by a compressed spring and a trigger. When said trigger is disengaged with said piston assembly said spring pushed said piston assembly and said needle into said barrel of said hypodermic syringe and holds said needle fixed to said piston assembly within said barrel thus preventing any accidental injection of bacteria, virus or other undesirable material into others. The disengagement of said trigger with said piston assembly is accomplished with only one and the same hand that is used to inject the needle of the syringe into a body.