An RFID tag for location inside a tubular base portion of a freestanding cryogenic vial, the RFID tag comprising: an RFID chip; an antenna connected to the chip; a support medium configured to support the chip and connected antenna; and a plug at least partially surrounding the chip, the antenna and the support medium, the plug being shaped to engage the tubular base portion of the vial. The RFID tag may be used to retrofit vials already stored at cryogenic temperatures.