The molecular nature of signal transduction in bacterial chemotaxis is virtually unknown. If the signal transduction is electrical in nature, an externally applied electric field should affect chemotactic behavior. We therefore studied the effect of an electromagnetically induced electric field on macroscopic assays of chemotaxis and motility of Escherichia coli. The electric field had opposing effects on these phenomena: it doubled motility, but inhibited chemotaxis by 70%. Controls for viability, for electrophoretic effects, and for other parameters that may affect chemotaxis, showed that this inhibition was specific for chemotaxis. These observations suggest that an electrical process may be involved in the chemotaxis machinery of E. coli. However, other interactions of the electric field with one or more of the membrane components of the chemotaxis machinery cannot be excluded.