An HgBr2/HgBr dissociation laser has been excited in ane‐beam preionized, self‐sustained discharge. Laser output of 100 mJ at 502 and 504 nm has been obtained with an overall efficiency of 0.5%. The steady‐state efficiency for formation of the HgBr (B) state in the Ne/N2/HgBr2discharge is determined to be 4%. An optical gain to loss ratio of ∼ 14 at the laser wavelength is inferred.