Galvanotaxis is the directional migration of a cell in an electric field, and has an important role in development and disease. Galvanotaxis is thought to be involved in the modulation of neural regeneration and glioma infiltration by endogenous electric fields, but the mechanisms that regulate the galvanotaxis of brain cells remain unknown. In their paper on page 2459, Peter Searson and colleagues investigate galvanotaxis in three different types of glial cells: fetal neural progenitor cells (fNPCs), astrocytes and brain-tumour-initiating cells (BTICs). The authors identify a crucial new role for cell surface heparan sulfate as a regulator of galvanotaxis. They show that all three cell types show a directional response to an external electric field, and, importantly, that heparan sulfate is localised towards the positive electrode of the cells regardless of cell type and direction of migration. Enzymatic digestion of heparan sulfate significantly attenuates cathodic galvanotaxis in fNPCs and BTICs. Moreover, it is unlikely that any single heparan sulfate proteoglycan is responsible for galvanotaxis; it is rather a collective outcome as a result of the localisation of heparan sulfate chains. Finally, Slit2, a chemorepulsive ligand, is found to be colocalised with heparan sulfate in forming a ligand gradient across cellular membranes. These results indicate that heparan sulfate is a new electrical-field sensor, and the authors propose a model in which galvanotaxis is mediated by the electrophoresis of heparan sulfate and its function as a co-receptor.