AbstractMotility of the marine gliding bacteriumFlexibacter polymorphuswas studied by using microcinematographic techniques. Following adhesion to a glass surface, multicellular filaments and individual cells usually began to glide within a few seconds at a speed of approximately 12 μm per second (at 23°C). Adhesion to the glass surface was evidently mediated by multitudes of extremely fine extracellular fibrils. Gliding velocity was independent of filament length but directly related to electron‐transport activity and substratum temperature in the range 3–35°C. The rate of gliding was inversely related to medium viscosity, suggesting that the locomotor apparatus functions at constant torque. Forward motion was occasionally interrupted by direction reversals, somersaults (observed primarily in single cells of short filaments), or spinning of filaments tethered by one pole. The frequency of direction reversal was found to be an inverse function of filament length. Translational motility was invariably accompanied by sinistral revolution about the longitudinal axis of a filament. The sense and pitch of revolution were constant among filaments of different length. Polystyrene microspheres or India ink particles adsorbed to gliding cells were actively displaced in either direction, their movement tracing either a regular zigzag or helical path along the filament surface. Because microspheres were also observed to move on nonmotile filaments, particle translocation was evidently not obligatorily linked to gliding locomotion. Multiple particles adsorbed to a single filament often moved independently. The data are consistent with a motility mechanism involving limited motion in numerous mechanically independent (yet functionally coordinated) domains on the cell surface.