SummaryTriamcinolone (20 pg per fetus) administered in utem to term rat fetuses (day 21 of gestation) increases the activities of renal GdPase and PEPCK. The absence (or marked decrease) of circulating corticosteroids in fetuses from adrenalectomizsd, metopirone-treated mothers has, however, no clear effect on the enzyme activities. Therefore, it is doubtful that corticosteroids play a role in the development of GdPase and PEPCK activities during the fetal period of life.