A liver slice system has been developed which actively incorporates labeled precursors into RNA and protein for as long as 10 h of incubation. The addition of glucocorticoid induces tyrosine aminotransferase (TA) in liver slices of hypophysectomized rats but not in liver homogenates of hypophysectomized rats or in slices derived from normal rats. TA activity is increased two- to sixfold during 6 h of incubation, the maximal response being observed with 10−6 M steroid. Addition of cydoheximide, at a concentration which depresses protein synthesis 95%, blocks the accumulation of TA. The half-life [Formula: see text] of induced TA is approximately 2–3 h and is similar to that of the basal, noninduced system. These data indicate that glucocorticoid acts only to increase the rate of TA synthesis without affecting its rate of degradation.