A double‐blind controlled trial was carried out to compare the effects of chenodeoxycholic acid (CDCA), ursodeoxycholic acid (UDCA), and placebo on cholesterol and triglyceride levels in patients with endogenous hypertriglyceridemias. The dose of both bile acids was four 150‐mg capsules a day. Total serum cholesterol levels did not show appreciable changes with any of the treatments. HDL cholesterol was significantly increased after CDCA but not after UDCA or placebo. CDCA feeding was associated with a significant decrease in serum triglyceride levels, whereas the other treatments failed to show an effect. It is concluded that UDCA does not affect serum lipid levels, whereas CDCA lowers serum triglycerides and may be useful in the treatment of endogenous hypertriglyceridemia.