The aim of this study was to assess the adaptive changes in plasma level of atrial natriuretic peptide(ANP) and its atrial mRNA expression in experimental rat model of chronic renal failure(CRF). Male Sprague-Dawley rats weighing 250-300g were divided into control rats, sham operated rats and 5/6 nephrectomized rats. CRF was induced by 5/6 nephrectomy, in that two thirds of the left kidney was ligated and the contralateral kidney was removed 1 week later. In the rats with 2/3 pole ligation, there were no significant changes in mean arterial pressure(MAP), heart rate, BUN and serum creatinine compared to sham operated rats. Expression of atrial ANP mRNA showed initially higher values and plasma renin activity(PRA) was lower than the sham operated rats. After 5/6 nephrectomy, MAP, heart rate, BUN and serum creatinine increased, and PRA showed the sustained lower values than the control rats. The changing pattern of plasma ANP level was similar to the that of ANP mRNA expression that showed biphasic peaks with the first increase at 1 to 3 days and the second increase at 28 days after nephrectomy. There were a significant positive correlation between plasma ANP level and MAP, and a negative correlation between plasma ANP and PRA. These results suggest that the secretion and the synthesis of ANP respond rapidly to the reduced renal mass, and ANP may play an important regulatory role during the renal adapting process in rats with experimental CRF.