In submaxillary glands, vas deferens, and cerebral cortex, [3H]prazosin labeled one homogeneous population of alpha 1-adrenergic receptors having a KD of 0.1 nM. Intravenous injections of phenoxybenzamine blocked these receptors in a dose-dependent manner without changing the affinity of the remaining sites for [3H]prazosin. The phenoxybenzamine efficiency was highest in submaxillary glands: 1 mg/kg completely blocked the alpha 1-adrenergic receptors but did not affect alpha 2-adrenergic, beta-adrenergic, and muscarinic receptors in this organ. After this blockade, the alpha-adrenergic receptors reappeared in the glands following a monoexponential time course. Analysis of this time course allows the determination of the rate constant for receptor degradation (k = 0.02 hr-1) and the rate of receptor production (r = 1.86 fmoles/mg of protein per hour). The half-life of the receptor was 33 hr. The reappearing receptors corresponded to newly synthetized receptors since their reappearance was blocked by i.p. injections of cycloheximide. Blockade of alpha 1-adrenergic receptors with phenoxybenzamine (2 mg/kg) did not affect receptor reappearance. In contrast, higher doses (4-20 mg/kg) decreased the velocity of receptor reappearance.