The effects of the anabolic steroid trenbolone acetate (TBA) on adrenal function and hepatic enzyme activity have been studied in growing female rats. Treatment with TBA resulted in a decrease in the peak of plasma corticosterone concentration which occurred during the afternoon. The enzymes tyrosine aminotransferase (TAT) and phosphoenol-pyruvate carboxykinase were measured in the livers of treated and control rats. Activities of both enzymes were maximal at 22.00 h, but that of TAT was reduced in TBA-treated rats. After injection of ACTH, TBA-treated rats showed a smaller increase in plasma corticosterone than did controls. Treatment with TBA did not affect the induction of TAT activity after corticosterone treatment. All TBA-treated rats grew significantly faster than controls and the possible relevance of this reduced adrenal function to the increased growth rate is discussed.