Tubular secretion appears to be a major route of the renal elimination of digoxin. Secretion of the drug by the tubules is modulated by renal blood flow, by a number of commonly coadministered drugs (e.g. quinidine, spironolactone, verapamil, amiodarone), and by age. The maximal transport capacity does not appear to be achieved with clinically relevant concentrations. The tubular transport of digoxin does not appear to be associated with the anionic or cationic transport systems, nor the Na+/K+-ATPase receptor. Further studies are needed to elucidate the exact mechanisms involved in the transtubular movement of the glycoside.