The influence of the thyrohormone status and of a nutrition rich in cholesterol on the hepatic enzymes glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, malate enzyme, and citrate cleavage enzyme was examined in female Wistar rats aged 3 and 18 months. Contrary to the findings in young animals, hyperthyreosis does not cause any significant increase in the activities of the malate enzyme and of the citrate cleavage enzyme. A nutrition rich in cholesterol induces a decrease of the activity of the malate enzyme in 3-month old rats; not, however, in the old rats.