The Poole–Frenkel effect was studied in xerographic carriers comprised of a soft-magnetic strontium ferrite core coated with 0 – 1.5 wt.% of polymethylmethacrylate (PMMA), either undoped, or doped with 6 wt.% of carbon black. DC current-voltage characteristics were measured in carriers formed into uniform compacts at two different levels of compacting force. Two types of Poole– Frenkel behavior were observed: the intrinsic Poole–Frenkel conduction of the carrier core, and the percolation effect, which arises at low compaction pressures due to insufficient interparticle contact. The percolation effect is believed to be the major cause of the non-Ohmic low voltage behavior of xerographic carriers in a magnetic brush. The percolation effect disappears at compaction pressures higher than typical compaction pressures in a magnetic brush, when the force at interparticle contacts becomes sufficient for the Ohmic conduction. Theoretical I-V curves were calculated on the basis of the non-linear equivalent circuit representing the conduction mechanisms in carriers, and showed a good agreement with the experimental data.