1. The effects of phenobarbitone on cholesterol and bile acid metabolism have been examined in healthy humans.
2. In three of four subjects the faecal excretion of bile acids was increased by phenobarbitone. This was associated with an increased pool size and turnover of cholic acid. Cholesterol excretion was not clearly affected. The fourth subject who did not respond was also exceptional in not showing an increase in the plasma clearance of antipyrine.
3. The three responsive subjects also developed significant increases in plasma cholesterol and triglyceride concentrations. These findings were associated with an early rise in very-low-density lipoprotein and a fall in plasma cholesterol specific radioactivity in one patient, changes compatible with increased cholesterol synthesis.