Studies of carnitine (CAR) export from intact rat liver indicate that this process is mediated by a specific, saturable transporter molecule (Sandor et al. 1985). The transporter itself has not been identified, but its properties are distinct from those of OCTN2, the major transport protein responsible for carnitine uptake (Kispal et al. 1987). The existence of a human transport reaction (again without an identified transporter) is inferred from the rat one.