Protein marker is a specific physiological indicator, left behind when a humanoid is host to a Goa'uld symbiote, at least when the symbiote allows itself to die without taking the host with it. Samantha Carter got a protein marker after she has been temporary host to Tok'ra Jolinar of Malkshur in 1998. (SG1: "In the Line of Duty") This protein was used to de-activate the machines infecting O'Neill and Frasier which were devised by Ma'chello. (SG1: "Holiday")

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