Abstract: An immersion probe for determination of the concentration of a gas dissolved in molten metal includes a probe body in the form of an elongated hermetically sealed housing. The body has a first end adapted to be connected to a gas inlet and a gas outlet, which first end may be hermetically sealed by a temporary sealing means. The body has a second end adapted to be immersed in molten metal, the second end is spaced from and in fluid flow communication with the first end and has a gas-permeable, liquid metal-impervious plug. The second end and the plug are hermetically sealed by a molten metal-soluble cap until melted during immersion into molten metal. An inert, dry carrier gas such as nitrogen or argon may be sealed within the probe body. A metal sleeve around the probe body, preferably of a composition fusible in and compatible with a molten metal being monitored may be used to provide a gas impermeable seal for the probe body.