Hole mobilities of N',N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD), TPD doped with 5, 6, 11, 12-tetraphenylnathacene (rubrene), and TPD doped with 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryle) 4H-pyran (DCM1) were measured by a time-of-flight (TOF) technique between 200 and 300 K. Pristine TPD has a hole mobility of about 2 x 10(-1) cm(2) V-1 s(-1) at room temperature. The corresponding TOF time transients were non-dispersive. Upon doping, the hole mobility decreased slightly for rubrene-doped TPD, and sharply for DCM1-doped TPD. The TOF time transients remain non-dispersive for both kind of doped samples. The dependence of the mobility on electric field and temperature for undoped and doped TPD was investigated. (C) 2002 Elsevier Science BY. All rights reserved.