The RalA binding protein 1 (RalBP1 or RLIP76) was originally identified as a GTP-RalA associated protein that acted as a downstream RalA effector in regulating Ral-Ras signaling). RalBP1 interacts with RalA and the endocytosis protein REPS2 (POB1) through its carboxy-terminal Ral binding domain. RalBP1 has an intrinsic GTPase activating function and interacts with Cdc42 through its centrally located Rho-GAP domain. A protein complex containing RalBP1/POB1/RalA regulates endocytosis of membrane receptors. RalBP1 also functions as a non-ABC transporter that catalyzes the ATP-dependent transport of numerous xenobiotics, including glutathione conjugates and some chemotherapeutic agents. RalBP1 transporter activity may play an important role in detoxification, drug resistance and the stress response). Increased expression of RalBP1 protein is associated with some forms of cancer and regression of cancer xenografts results from RalBP1 inhibition. Evidence to date suggests that RalBP1 may be a promising therapeutic target for cancer therapy.