The renal clearances of digoxin, creatinine, and urea nitrogen were determined simultaneously in each of 41 patients receiving digoxin, in most of whom there was prerenal azotemia. Mean ± SD values were: blood urea nitrogen (RUN), 26.1 ± 12.8 mg per 100 ml; creatinine, 1.1 + 0041 mg per 100 ml; creatinine clearance, 78 ± 42 ml/min/1.73 m2; digoxin clearance, 66.6 ± 42.1 ml/min/1.73 m2; urea nitrogen clearance, 27.8 ± 19.2 ml/min/1.73 m2. Correlation analysis revealed that urea clearance is superior to creatinine clearance, and RUN is superior to serum creatinine concentration in the degree of relationship to renal digoxin clearance. Moreover, using partial correlation techniques, it is apparent that in these patients digoxin clearance was significantly related to urine flow rate independent of creatinine clearance, and to urea nitrogen clearance independent of both creatinine clearance and urine flow rate. These findings are compatible with the hypo thesis that digoxin undergoes some degree of tubular reabsorption as welt as filtration and secretion.