In two double-blind studies with 24 and 12 patients, respectively, the effect of silymarine on chronic hepatitis was studied. The treatment lasted three months to one year. In the laboratory tests investigated no remarkable difference between silymarine and placebo therapy was seen. Some histological changes, however, were improved under silymarine, one of them significantly. A control of these findings will be necessary. The question arises if silymarine occupies receptors on the liver cell membrane and therefore causes a partial blocking of immunologic reactions. The difficulties of prospective studies in chronic liver disease are emphasized.