Abstract: A test tube, suitable to be immersed in a cryogenic fluid, comprises a containing body having a perimeter wall that defines a containing compartment, a bottom wall, disposed inside the latter to close it at the lower part, and a housing seating, inside the perimeter wall and outside the containing compartment. A support element for an identification code is suitable to be inserted into the housing seating, with at least a free surface facing toward the outside of the housing seating on the opposite side with respect to the bottom wall. In correspondence to said housing seating, mechanical constraint means are provided in cooperation with said perimeter wall of the containing body and with a peripheral portion of the free surface of the support element, in order to constrain the latter in a defined axial position with respect to the containing body.