1. In order to study the effects of chenodeoxycholic acid on serum and biliary lipids in hyperlipoproteinaemia, chenodeoxycholic acid was administered to seven type IIa, eight type IIb and eight type IV patients in a daily dose of 750 mg (1·9 mmol) for 3 months.
2. The serum concentrations of cholesterol and triglycerides were determined at 4-week intervals: cholesterol remained unchanged whereas triglycerides decreased 15–20%.
3. In 17 patients, biliary lipids were studied. The proportion of chenodeoxycholic acid in the bile increased to about 70%; lithocholic acid and ursodeoxycholic acid increased significantly.
4. Bile saturation with cholesterol decreased and correlated negatively with the proportion of chenodeoxycholic acid in biliary bile acids but positively with serum triglycerides.
5. It is concluded that chenodeoxycholic acid treatment in hyperlipoproteinaemia is associated with a parallel fall in serum triglycerides and biliary cholesterol and thus may prove to be a useful adjunct in hypolipidaemic treatment.