For the purpose of elucidating charge transport in disordered organic materials, hole transport in the glassy state of 4-diphenylaminobenzaldehyde diphenylhydrazone (DPH), 4-diphenylaminobenzaldehyde methylphenylhydrazone (DPMH), and DPH doped with a small amount of 4-diethylaminobenzaldehyde diphenylhydrazone (DEH) has been studied. The hole drift mobility in the DPMH glass was approximately one-fifth of that in the DPH glass; this was attributed to a higher activation energy in terms of the Arrhenius formalism or to an increased width of the Gaussian density of states based on the site energy disorder model for the DPMH glass. The introduction of less than 1 mol% DEH into DPH resulted in a significant increase in activation energy or in the Gaussian width of the site energy distribution, which increased with increasing concentration of the dopant.