In the present study expression levels of secretin and secretin receptor mRNAs in several brain regions of rats ranging in age from postnatal days 7 to 60 were investigated by quantitative real-time PCR. Expression of secretin and secretin receptor was detected in the central amygdala, hippocampus, area postrema, nucleus of the tractus solitary and cerebellum. The cerebellum expressed secretin receptor at significantly higher levels than that found in other brain regions within all the ages examined. In contrast, secretin mRNA was significantly higher in the nucleus of the tractus solitary than in the other four brain regions examined in postnatal day-21, -30 and -60 rats. Within most brain regions, both secretin and secretin receptor mRNAs were more abundant in postnatal day-7 and -14 rats as compared to postnatal day-21, -30 and -60 rats. Thus, secretin and its receptor are widely expressed in rat brain and the expression of both genes is developmentally regulated during the first few weeks following birth.