The aim of the present study was to evaluate plasma renin activity (PRA) and Angiotensin (Ang) levels [Ang I, Ang II and Ang-(1-7)] to examine the circulating Renin-Angiotensin System (RAS) in renal disease among children with different forms and stages of chronic renal failure (CRF). Subjects were divided as follows: 32 normotensive healthy subjects, 23 normotensive CRF subjects, 34 hypertensive CRF subjects and 21 subjects with end-stage renal disease (ESRD). Radioimmunoassays for PRA (ngAngI/mL/h) and angiotensin (pg/mL) measurements were performed on all subjects. PRA, Ang I, Ang II and Ang-(1-7) levels were significantly higher in hypertensive CRF subjects when compared with normotensive CRF and healthy subjects (p < 0.05 for all comparisons). No differences were observed between normotensive CRF and healthy subjects. ESRD subjects exhibited a dramatic increase in Ang-(1-7) (25-fold higher than control values). In hypertensive CRF subjects, treatment with angiotensin-converting enzyme inhibitors (ACEi) increased (1.4-fold) plasma Ang-(1-7) and decreased (2.4-fold) Ang II. In ESRD, the use of ACEi produced a similar (1.5-fold) elevation of Ang-(1-7), but no changes in plasma Ang II. Our data showed different circulating RAS profiles between hypertensive and in normotensive CRF subjects. Marked changes in plasma Ang-(1-7) were associated with the presence of hypertension and progression of kidney dysfunction.