Objective To evaluate the role of endogenous ouabain(EO)In the development of hypertension and the characteristics of EO secretion in 1k1c(one kidney, one clipped) hypertensive rats. Methods EO content of serum and tissues in 1k1c hypertensive rats and normal control Sprague-Dawley (SD) rats was detected by the method of enzyme linked immunosorbent assay (ELISA). The relationship between serum or tissue ouabain and blood pressure was analyzed in 1k1c hypertensive rats. Results The ouabain content of serum, heart, kidney, adrenal gland, pituitary and hypothalamus was significantly higher in 1k1c hypertensive rats then that in normal control SD rats (2.25, 2.63, 3.35,40.37,3.34,15.7μg/kg tissue in 1k1c hypertensive rats vs 1.12, 1.79, 1.73, 27.54, 1.83, 10.10μg/kg tissue in control SD rats, respectively. P<0.05 for all of these comparisons). The ouabain content of the adrenal gland and the hypothalamus was higher than that of other tissues or serum, both in 1k1c rats and in control SD rats. The EO content of serum, kidney and hypothalamus was significantly correlated with blood pressure in 1k1c hypertensive rats (r=0.59,0.63,0.52, respectively. P<0.05). The ouabain content of heart, liver, adrenal gland and pituitary was not correlated with blood pressure. Conclusions EO might play an important role in the development of hypertension in 1k1c hypertensive rats. The adrenal gland may be a major source of EO and the hypothalamus-pituitary-adrenal axis may be involved in the regulation of EO secretion.