[3H]prazosin (PRAZ) and [3H]rauwolscine (RAUW) were used to examine the ontogeny of renal alpha 1- and alpha 2-adrenoceptors in the inbred Dahl hypertension-sensitive (S/JR) and -resistant (R/JR) rat. PRAZ and RAUW each bound to a single population of non-interacting sites. The binding of each ligand was saturable and reversible. The greatest proliferation of each receptor subtype occurred between 5 and 25 days of age. During this period, a 4 to 5-fold increase in the density of each was observed. Adult levels of each were reached by 50 days of age. The alpha 2-adrenoceptor was the predominant subtype present in renal tissue. However, its ratio to the alpha 1 subtype was influenced by strain and age: the ratio was greatest in the S/JR strain and decreased with age in both strains. The profile of alpha 1-adrenoceptor development was similar in S/JR and R/JR rats. In contrast, the density of alpha 2-adrenoceptors was similar in S/JR and R/JR rats at 5 and 15 days of age but significantly greater in the S/JR rat between 25 and 150 days of age. The elevated density of alpha 2-adrenoceptors could not be explained by strain-related differences in blood pressure or alterations in the affinity of the receptor. The results suggest that a relationship may exist between elevated renal alpha 2-adrenoceptor density and the genetic predisposition to hypertension in the S/JR rat. However, because this relationship is not apparent during the neonatal period of development, the possibility that the elevated density of sites may be secondary to some other event should also be considered.