Substituent effects on the hole-drift mobility of N,N,N',N'-tetraarylphenylenediamine derivatives have been investigated. The hole mobility values are dependent on the number of methyl substituents and their position in the investigated transporting materials (TM). The highest mobility was observed in the TM containing methyl groups at the para positions of the side benzene rings and at the central ring. On the other hand, the priority of the m-phenylenediamine derivative against the p-phenylenediamine homologue was proved.