Deuridium is a rare element used by the Kobliad.
The Kobliad are a dying race, and use deuridium supplied to them by the Federation to prolong their life-spans by replenishing their cell structures.
In 2369, the Federation cargo ship Norkova was transporting a shipment of deuridium to Deep Space 9 from the Gamma Quadrant for transport to the Kobliad homeworld. Just after exiting the wormhole, Rao Vantika (in the body of Doctor Bashir) took control of the Norkova and tried to steal the shipment, but was stopped when Doctor Bashir was able to regain control. (DS9: "The Passenger")