In previous studies we have shown that patients or rats with chronic renal failure display reduced blood pressure response to norepinephrine (NE). This abnormality is related to the high levels of parathyroid hormone (PTH) which stimulates vasodilator prostaglandin production. To determine whether chronic renal failure (CRF) also affects pressor response to NE through changes in the properties of alpha 1 adrenoceptors, we have measured plasma NE and the number of binding sited (Bmax) and the KD of these receptors in isolated mesenteric arteries of normal CRF rats and of CRF rats previously parathyroidectomized (PTX). Plasma NE was greater (P less than 0.01) in CRF than in control (67 +/- 14 vs. 32 +/- 3.1 ng/dl), but it was not different from CRF-PTX rats. The Bmax of alpha 1 adrenoceptors was lower (P less than 0.05) in CRF than control (80 +/- 10 vs. 173 +/- 29 fmol/mg protein), but it was similar in CRF and CRF-PTX rats. The KD was not significantly different among the three groups of rats studied. The data show that the number of alpha 1 adrenoceptors is reduced in CRF and this is not related to excess PTH. This abnormality may contribute to the reduced pressor response to NE in CRF. The effect of PTH, on the vascular response to NE is not related to changes in plasma levels of NE or in binding sites for NE.