This short review considers the mechanisms of organic anion secretion in renal proximal tubules. Particular attention is given to the energy coupling of p-aminohippurate transport to inorganic anion gradients generated across both basolateral and brush-border membranes. The coupling is considered to be a consequence of the combined operation of the co-transport and anion-exchange mechanisms. A possible coexistence of several organic anion pathways with overlapping substrate specificity and/or energetic dependence of the total ion gradient are suggested. The problem of identification of transporters involved in organic anion secretion is discussed.