A mechanism is proposed to explain the improvement in discharge uniformity observed in pure electric‐discharge‐pumped rare‐gas halide lasers when a uv preionizer is used to precondition the laser medium. In the model the F−ions formed by dissociative attachment following uv photoionization act as a reservoir from which electrons are easily released when the main discharge field is applied. The model shows that a time delay is required between the application of the uv and the main discharge, and also that the effect of the preionizer can last some tens of microseconds despite the large electron attachment rates in the laser mixture.