Drugs known to block impulse transmittance, or that depolarize membranes, severely affected motility in Rhodospirillum rubrum and Thiospirillum jenense. Procain, serotonine creatinine sulfate, neostigmine methyl sulfate, eserine sulfate, atropin sulfate, parathion, acetylcholine chloride, and mersalyl acid, all were active in this respect. It is suggested that a system involving electrical potential differences in bacterial membranes may possibly play a role in bacterial flagellar motility.