This article considers the interactions between drugs and renal function, first, the adverse effects of nephrotoxic drugs and the changes in drug response associated with renal failure. It then discusses drugs intended to alter urinary sodium excretion (diuretics) and urinary pH as well as drugs which alter renal concentrating and diluting capacity. In each case emphasis is placed on the relationship between the drug effects and normal renal mechanisms. Reasons for the special vulnerability of the kidney to the toxic effects of drugs (e.g. antibiotics) are discussed and the practical problems of adjustment of drug dosage according to renal function are indicated. Finally, consideration is given to drugs, notably oral sorbents, which can partially substitute for renal function and might therefore eventually prove ideal for the management of advanced renal failure in small animals.