We studied the effect of spirochete Borrelia burgdorferi sensu lato cell membrane proteins on excitability of myelinated nerve fiber. It was found that cell surface proteins of spirochetes B. burgdorferi s. s. bind to Ranvier nodes of the axon and to Schwann cells. Binding of B. burgdorferi s. s. and B. garinii to the nerve fiber modulates the amplitude and conduction velocity of the action potential, while B. afzelii had no effect on these parameters. The decrease in the spike amplitude and conduction velocity during sorption of B. burgdorferi s. s. or cell wall proteins was accompanied by desorption of membrane-bound calcium.