Erythropoietin (Epo) gene expression in ovine fetal liver and kidneys was measured by competitive RT-PCR in situations in which fetal glucocorticoid status was altered. Bilateral adrenalectomy at 120 +/- 0.3 days gestation (term is 145-150 days) caused a significant (P < 0.05) 5-fold increase in renal Epo messenger RNA (mRNA) levels at 145 +/- 1 days compared to those in age-matched controls. With cortisol replacement in adrenalectomized fetuses, renal Epo mRNA levels dropped to 17% of this values (P < 0.05). Cortisol infusion (230 micrograms/h for 48 h) at 108 +/- 1 day decreased renal Epo gene expression significantly (P < 0.01) to 23% of the control value; dexamethasone treatment of the ewe at midgestation (0.76 mg/h for 48 h) also decreased fetal, but not adult, renal Epo mRNA levels (to 12% of control value; P < 0.01). Fetal and maternal liver Epo mRNA levels were unaffected by glucocorticoid status at any stage of pregnancy. Thus, glucocorticoids can influence fetal renal, but not maternal, Epo gene expression. In the presence of high concentrations of fetal glucocorticoids, plasma Epo values were consistently 4-5 mU/ml, close to the sensitivity of the assay, whereas in seven adrenalectomized fetuses, the plasma Epo value was 9.1 +/- 1.4 mU/ml.