Various Ca²⁺ antagonists used in animal research, many of them known to be Ca²⁺ channel blockers, inhibited Escherichia coli chemotaxis (measured as entry of cells into a capillary containing attractant). The most effective of these, acting in the nanomolar range, was -conotoxin GVIA. The next most effective were gallopamil and verapamil. At concentrations around 100-fold higher than that needed for inhibition of chemotaxis, each of these antagonists inhibited motility (measured as entry of cells into a capillary lacking attractant). Various other Ca²⁺ antagonists were less effective, though chemotaxis was almost always more sensitive to inhibition than was motility. Cells treated with each of these Ca²⁺ antagonists swam with a running bias, i.e., tumbling was inhibited. Similarly, some Na⁺ antagonists used in animal research inhibited bacterial chemotaxis. E. coli chemotaxis was inhibited by saxitoxin at concentrations above 10⁷ M, while more than 10⁴ M was needed to inhibit motility. Cells treated with saxitoxin swam with a tumbling bias. In the case of other Na⁺ antagonists in animals, aconitine inhibited bacterial chemotaxis 10 times more effectively than it inhibited motility, and two others inhibited chemotaxis and motility at about the same concentration. In the case of K⁺ antagonists used in animal research, 4-aminopyridine blocked E. coli chemotaxis between 10³ M and, totally, 10² M, while motility was not affected at 10² M; on the other hand, tetraethylammonium chloride failed to inhibit either chemotaxis or motility at 10² M.