Opto-galvanic effect in the He-Cd+ hollow cathode discharge tube was experimentally studied. The dependence of the opto-galvanic signal (OGS) on the laser power, the discharge current and the position along the laser tube are presented. The possible mechanisms of OGS are discussed. It is found that OGS could be used in measuring the homogeneity and stability of the Cd+ concentration along the laser tube.