The influence of oxidizing treatments on the photorefractive properties of nominally pure ferroelectric lead germanate crystals is investigated. In two-wave mixing experiments the dark conductivity, the intensity dependence of the photoconductivity, the effective charge density and the factors that reduce the space-charge field are determined. Oxidizing treatments increase the photoconductivity and the effective charge density, but decrease the electron-hole-competition factor. The experimental results can be explained in terms of a one-center model with electron-hole competition. © 2001 OPA (Overseas Publishers Association) N.V.