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A glow discharge technique has been developed and 3 applied to the conditioning of the large (38 m) Poloidal Divertor Experiment (PDX) vacuum vessel. The dis charge parameters and working gas (H ?) were chosen to maximize C and 0 removal and minimize metal sputtering. The glow discharge was produced by biasing one or two internal anodes at 400 V to sustain a discharge current of 2^4 A per anode. Purified H. at a pressure of 3 x10 torr was flowed through PDX at "10 t-a/s. The effectiveness oi the glow discharge conditioning was monitored by measuring impurity gas (CH,, C_H., and CO) exhaust rates by mass spectrometry and C and O surface removal rates by in-situ AES and XPS. Initial glow dis charge operation was accompanied by frequent arcing which subsequenty decreased with time. Low Z (= 2) high power discharges were obtained in PDX after 120 hours of glow discharge treatment, during which more than 100 equi valent monolayers of C and 0 were removed from the vessel.