Escherichia coli DNAtopoisomeraseIinhibition, binding to B-DNA duplex, and antibacterial activity has been evaluated. Bisbenzimidazoles with alkynyl side chains display excellent E. coli DNAtopoisomeraseIinhibition properties with IC50 values <5.0 μM. Several bisbenzimidazoles (3, 6, 7, 8) also inhibit RNA topoisomerase activity of E. coli DNAtopoisomeraseI. Bisbenzimidazoles inhibit bacterial growth