Expression of the mouse renin genes (Ren1 and Ren2) in the submaxillary gland of female mice has been analyzed following administration of thyroxine (T4) or dihydrotestosterone (DHT). Both hormones appear to act independently on mRNA accumulation which increases about 5 fold over basal level. In vitro transcription assays in isolated nuclei demonstrate that both hormones act at the transcriptional level. The effects of DHT and T4 were also analyzed in transgenic mice obtained by microinjection of the Ren2 gene. We show that T4 is as efficient as DHT in promoting renin mRNA accumulation in these transgenic animals, in spite of their low basal level of Ren2 mRNA. Structural comparison of the Ren1 and Ren2 promoters with those of other genes regulated by T4 shows the conservation of two discrete regions.