Digoxin absorption has been studied in four normal volunteers. Whereas the digoxin (Lanoxin) administered in an oral solution is completely absorbed, that in tablet form is only 75% absorbed. These results are obtained from the cumulative urinary excretion of digoxin rather than serum digoxin concentration curves since the digoxin radioimmunoassay is not sensitive enough to obtain valid data by the latter method. Since digoxin has a steep dose-response curve, a reduction in digoxin dosage is necessary when changing from oral tablet to parenteral administration to avoid the development of digoxin toxicity.