Patients suffering from cerebrotendinous xanthomatosis, an inborn error of metabolism in bile acid synthesis, were given oral treatment with chenodeoxycholic acid, ursodeoxycholic acid, cholic acid and taurocholic acid. The effectiveness of the different therapies was evaluated by measuring the urinary excretion of 5 beta-cholestane-3 alpha,7 alpha,12 alpha,23,25-pentol, which should decrease, when the administered bile acid is able to suppress endogenous bile acid synthesis. From the results it is concluded that chenodeoxycholic acid and cholic acid activate the bile acid negative feedback mechanism, contrary to ursodeoxycholic acid and taurine conjugated cholic acid. Either cholic acid or chenodeoxycholic acid are the therapies of choice for the treatment of cerebrotendinous xanthomatosis. For various reasons the use of cholic acid is especially recommended.