Abstract 1. 1. The succinate dehydrogenase (SDH) and d-3-hydroxybutyrate dehydrogenase (HBDH) activities were measured over a 24-hr period in rat liver mitochondria after chronic alcohol ingestion and withdrawal. 2. 2. The diurnal patterns of both the enzyme activities were shown to change after alcohol consumption, with 64–66% decrease in the daily mean levels. 3. 3. The diurnal rhythms of the SDH and HBDH activities are partially restored 24–72 hr after alcohol withdrawal. 4. 4. There was no correlation between changes in both the enzyme activities and the NAD +/NADH ratio of liver mitochondria from control, ethanol-fed and withdrawn rats over the day.