The drift of a small photoinjected sheet of free carriers can be used as a probe of the space charge and internal field distributions in the bulk of amorphous selenium films. We have found that unneutralized space charge can exist for long periods of time and can significantly affect the measurement of both drift mobility and deep trapping lifetimes. By deliberately creating bulk space charge, we can also examine some of the fatigue effects that arise when a selenium photoreceptor is not allowed to relax between large variations in applied field and exposure.