Abstract Androgens regulate blood pressure and renal α 2 -adrenergic receptors in a parallel fashion in the spontaneously hypertensive rat (SHR). The present studies investigated whether this regulation of renal α 2B -adrenergic receptors occurs at the mRNA level. Male and female SHR were gonadectomized at 4 weeks of age. The gonadectomized rats were implanted with or without testosterone propionate. Sham- gonadectomized rats served as controls. Total kidney RNA was purified, and α 2B -adrenergic receptor mRNA was quantified with a reverse transcriptase–polymerase chain reaction (RT-PCR) assay. The assay uses a mimic RNA added at known concentrations to the sample RNA. The mimic was constructed from the target sequence in the α 2B -adrenergic receptor mRNA plus a 20-bp insertion of a random nucleotide sequence. The amount of α 2B -adrenergic receptor mRNA present in each sample was obtained by determining the equivalence point between the amount of RT-PCR product formed in the target band versus the mimic band, which were resolved by gel electrophoresis. Intact males had more than two times as much α 2B -adrenergic receptor mRNA as intact females. Castration of males reduced the male-female difference by more than 60%. Ovariectomy slightly increased the α 2B -adrenergic receptor mRNA level compared with that of intact females. Treatment with testosterone elevated α 2B -adrenergic receptor mRNA levels of gonadectomized males and females to the level of intact males. The α 2B -adrenergic receptor mRNA levels correlated remarkably well with renal α 2 -adrenergic receptor density. We conclude that testosterone regulates renal α 2B -adrenergic receptor gene expression at the mRNA level in the SHR.