Objective To investigate the changes of blood and urine endothelin levels in the aged patients with primary nephrotic syndrome(PNS) and their clinical significance. Methods The levels of blood and urine endothelin were measured by radioimmunoassay at different stages(active and alleviated stages) in 40 elderly and 40 non elderly patients with PNS and 40 elderly healthy controls(control group). The levels of endothelin in blood and urine of the aged patients with PNS, and serum creatinine(Scr), endogenous creatinine clearance rate(Ccr), 24 hour urinary protein and urinary retinal binding protein(uRBP) were determined. Results The contents of endothelin in blood and urine of the aged PNS patients in the active stage were (229?81) ng/L and (143?58)ng/24 h,which were apparently higher than those in the alleviated stage 〔(60?11) ng/L, (53?13)ng/24 h〕 and the healthy control group〔(53?9) ng/L, (50?14 ng)/24 h, P 0 05). Conclusions Endothelin may be involved in the pathogenesis of the aged PNS. The increased urine endothelin level may be an important factor in glomerulus and tubular damage in the elderly PNS patients.