1. The extent of reversal of baroreceptor resetting after pressure normalization was studied in rats with renal hypertension of up to 6 months duration. The aortas of these rats when compared with those of 2 month hypertensive rats were thicker (44%) and had a larger calibre (29%).

2. The more severe morphological alterations found in the 6 month hypertensive rats did not interfere with the reversibility of the resetting process. The entire range of pressure for baroreceptor activation showed a small downward displacement after 1 h and was functioning at a completely normal pressure 6 h after pressure normalization.

3. The data show that reversal of resetting from hypertension is a very rapid process that is independent of the duration of hypertension and the severity of morphological lesions. Moreover, they indicate that reversal is a permanent phenomenon because it was also observed after 2 days of pressure normalization.

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