Most cell biologists think about the reorganization of actin and other cytoskeletal molecules when they think about cell migration. However, data from Alan Verkman and colleagues suggest that the influx of water through aquaporin 4, a water-selective channel at the leading edge of migrating astroglia, can also be involved (see p. 5691). Aquaporin 4 facilitates movement of water in and out of the brain. When the authors studied the migratory behaviour of astroglia isolated from mouse neocortex, however, they discovered a new role for this protein. Although astroglia from aquaporin-4-null mice behave like those from wild-type mice in many respects, their migration is impaired. In addition, the knockout mice have difficulty forming glial scars, because reactive astroglia fail to migrate normally after a cortical stab injury. Given that glial scarring reduces neuronal regeneration after injury, the authors suggest that inhibiting aquaporin 4 might provide a new way to treat central nervous system injuries.