We evaluated the urinary excretion of immunoreactive endogenous ouabain-like factor (OLF) and digoxin-like factor (DLF) to investigate their pathophysiological roles in sodium metabolism and blood pressure in 5/6-reduced renal mass rats, a model of volume-expanded hypertension. About five-sixths of the kidney mass (5/6 RRM, n = 9) was removed from male Sprague-Dawley rats, or the rats were sham operated (control, n = 10). Both groups were fed regular diets with tap water for 1 wk as a control period, followed by 1% saline solution for 4 wk. Systolic blood pressure (SBP), urine volume (UV), urinary sodium excretion (UNaV), DLF, and OLF were measured on the last 2 d of every week throughout the experimental period. SBP and UNaV were significantly higher in 5/6 RRM rats than in control rats. Urinary DLF significantly increased, reaching peak value in the first week, while OLF increased continuously, reaching peak value in the fourth week. In the first week, there were a significant positive correlations between the change in DLF and the changes in UNaV and SBP. However, the change in OLF was not correlated with changes in either UNaV or SBP. Both SBP and UNaV showed a significant positive correlation with OLF (p<0.001, r=0.547, p<0.001, r=0.658, respectively), whereas DLF significantly correlated with UNaV (p< 0.001, r= 0.584) but not with SBP in 5/6 RRM. These findings suggest that endogenous OLF and DLF coexist in rat urine and that an increased level of OLF, but not DLF, may contribute to the development and maintenance of hypertension. DLF may contribute to renal sodium excretion in this volume-expanded hypertensive rat model.