It has been well known that the renal cortical blood flow rate was much higher than that of the medulla and the renal blood flow distribution was affected by hemorrhage, volume expansion or salt-loading. The existance of the heterogeneities of glomerular filtration rate and nephron has also been reported. In order to understand the regulations and physiological roles of the heterogeneities, studies on the intrarenal renin-angiotensin system have been focused. Although it is well known that the granularity of iuxtaglomerular cells and renal renin content are more marked in superficial than in the deep glomeruli, their physiological significance is not quite clear. This study was therefore undertaken to clarify changes in renin response and isoelectric ronin profile to TMB-8 in outer, mid and inner cotices of normotensive and hypertensive rats. The basal rate of renin release was highest in outer cortex of Sprague-Dawley rat (SDR), Wistar rat (WR) and spontaneously hypertensive rat (SHR). The basal renin release from outer and inner cortex of SHR was significantly lower than that from those of SDR. The reponse of renin release to TM8-8 was highest in mid cortex and the increase of renin release in response to TMB-8 from inner cortex of SDR was significantly higher than that in SHR. In dehydrated rats, the basal renin release from renal cortical slices of SDR was increased but that from WR and SHR was not. The response of renin release to TMB-8 from mid and inner cortex of dehydrated WR tended to increase. In dehyrated SHR, increase of renin release from inner cortex was significantly higher than that in euhydrated SHR. No significant differences in the isoelectric renin profile were found both in different cortical areas and strains. In dehydrated rats, the percentage of renin form 2 was decreased and those of renin form 5 and 6 were increased. These results suggest that the heterogeneity of renin release from cortical area of euhydrated and dehydrated rats in response to TMB-8 may be related to the changes of renal blood flow and/or calcium metabolism in cortical area. These data also suggest that the renin forms with different isoelectric points may have an physiological significance.