The decrease of the hole mobility in polycarbonate doped with 17% of a triphenylaminobenzene derivative at electric fields exceeding 1.0 × 106Vcm−1is rationalized in the framework of the Marcus theory. By analysis of the mobility data in the framework of the expression, derived by Marcus and relating the free energy of election transfer to the free activation energy of this process, the average hopping distance, the reorganisation energy and the barrierless electron transfer rate constant could be obtained. In this way physical acceptable values, amounting to 2.7nm, 0.33eV, 4.88 × 106s−1, were found for the respective parameters at room temperature.