BACKGROUND: The ontogeny of the renal mineralocorticoid (MR) and glucocorticoid (GR) receptors in the ovine fetus, and the effects of early exposure to synthetic or natural glucocorticoids on the expression of these genes in late gestation were examined. METHODS: A partial cDNA sequence for the ovine MR was cloned and used to generate primers and probes to measure MR mRNA expression by real-time polymerase chain reaction (PCR). GR mRNA was also measured. Kidneys were collected from ovine fetuses at various stages of gestation (days 60 to 140), twin ovine fetuses at 130 days, from ewes treated at days 26 to 28 with either saline, dexamethasone or cortisol, and adult sheep. Ligand binding was used to determine both GR and MR protein levels in all 130-day-old fetuses and adults. RESULTS: No significant changes in the expression of either renal MR or GR were detected throughout gestation. Cytosolic protein levels were higher in the fetal kidneys than in the adult. There was a significant increase in both fetal MR and GR mRNA expression, but not protein levels in kidneys from ewes pretreated with dexamethasone. CONCLUSIONS: MR and GR mRNA are expressed throughout development in ovine fetal kidneys. Dexamethasone treatment resulted in increased expression of MR and GR mRNA but not protein levels. The dissociation between fetal mRNA and protein levels, relative to adult kidneys, suggests that it may be confounding to draw conclusions based on mRNA levels alone.