The migration of Lyme disease spirochetes (Borrelia burgdorferi) toward salivary gland extracts (SGEs) of vector ticks was determined by a modified U-tube chemotaxis assay. Responses of cultured spirochetes to the SGEs were measured by dark-field microscopy at intervals after the initial inoculation. The average numbers of spirochetes that migrated were compared between U-tubes containing either SGEs or phosphate-buffered saline (PBS). Spirochetes showed increased migration in tubes containing SGE, and migration was approximately 10-20-fold higher than that for spirochetes observed in tubes containing PBS. In addition, the span of migration showed no significant difference relative to the origin of spirochete isolation. These results demonstrate that spirochete migration can be enhanced by SGEs from fed vector ticks. This mechanism may contribute to the novel transmission of Lyme disease spirochetes between cofeeding infected and uninfected ticks in nature.