This antiserum selectively binds to drebrin, a ubiquitous actin-binding protein with a molecular weight of 70 kD (SDS-PAGE mobility indicates Mr 120,000). Initially found only in neuronal cells, drebrin is now known to also exist in the actin-rich lamellipodia and filopodia of motile cells. It is concentrated at junctional plaques, forming a unique microfilament anchoring system in polar epithelial cells.