This review focuses on sodium-independent transport systems for organic cations in small intestine, liver, kidney, and brain. The roles of P-glycoproteins (MDR) and anion transporters (OATP) in organic cation transport are reported, and two members of the new transporter family OCT are described. The OCT transporters belong to a superfamily that includes multidrug-resistance proteins, facilitative diffusion systems, and proton antiporters. They mediate electrogenic transport of small organic cations with different molecular structures, independently of sodium and proton gradients. The current knowledge of the distribution and functional properties of cloned cation transport systems and of cation transport measured in intact plasma membranes is used to postulate identical or homologous transporters in intestine, liver, kidney, and brain.