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 that mediates this process in human tissues has not been identified, but its properties are distinct from those of SLC22A5 / OCTN2, the major transport protein responsible for carnitine uptake (Tamai et al. 1998; Wu et al. 1999). Indeed, as noted by Vaz & Wanders (2002), export of carnitine and its metabolites is probably mediated by another transport system, or possibly by passive diffusion.