Abstract Several types of benzimidazole derivatives were prepared and were screened for H 1-antihistaminic activity. Most of the compounds showed potent antihistaminic activity in vitro. Among them 2-[(1-piperazinyl) methyl]-benzimidazoles 14 and 2-[(1-homopiperazinyi) methyl] benzimidazoles 15 exhibited potent activity also in vivo.