The present review is mainly concerned with the transport mechanisms of drugs in the plasma membranes of the renal epithelial cells. Organic anions and cations are actively secreted from plasma to filtrate in the proximal tubules. Studies with isolated membrane vesicles have generated a great deal of information about the transport mechanisms of organic ions in basolateral and brush-border membranes. p-Aminohippurate (PAH ; an organic anion) is actively transported in basolateral membranes by two functionally linked transport systems, Na⁺/dicarboxylate cotransporter and dicarboxylate/PA H exchanger. In rat brush-border membranes, PAH is probably transported by two distinct transport systems, anion exchanger and potential-sensitive transport system. On the other hand, tetraethylammonium (TEA ; an organic cation) is transported by a potential-sensitive, carrier-mediated system in basolateral membranes. In brush-border membranes, TEA is actively transported by H⁺/TEA antiport system. Thus, the vesicle studies have provided new insights into our understanding of renal tubular transport mechanisms of drugs.