Abstract: A non-reusable hypodermic syringe which comprises a cylinder and a plunger, spaced from the lower end portion of the cylinder there is provided a first half of a one-directional retention means. The plunger comprises a shaft and a piston attached to an end of the shaft, and the second half of the retention means is provided on the shaft close to the connection of the piston. The retention means allows the full insertion of the plunger in the cylinder but impedes its withdrawal. Preferably, a projection ring is provided just above the retention means on the inner cylinder wall that indicates to the user that further movement to insert the plunger will positively engage the retention means. This projection ring acts as a tactile warning to the user to prevent "accidental" engagement of the retention means when filling the syringe.