The effect of Beta-Sitosterol (Sitosterin Delalande) on plasma lipids in 20 pretreated patients with type IIa and IIb familial hyperlipoproteinemia is reported. 6-18 g of the drug were given for a time of two to twelve months. In 11 patients the plasma cholesterol level decreased between 10 and 30%. Since Beta-Sitosterol has no effect on plasma triglycerides, an additional hypertriglyceridemia must be taken care of and treated if necessary. Beta-Sitosterol can be called an effective substance in the treatment of hypercholesterinemia. In addition the diet cure becomes easier.