Recently the use of herbal preparations as remedies for various medical conditions, has been rapidly increasing in Korea. In our previous study, 38.9% of patients with chronic liver disease were found to use some sorts of herbal preparations. They believe herbal preparations are safe although the ingredients has never been rigorously substantiated. Toxicities of certain herbal preparations are caused by their contaminants and adulterated ingredients or concurrently used conventional drugs rather than specific components of the herbal preparations. Furthermore, in most instances, multiple herbal ingredients are used by the prescribers of oriental medicine. All of these conditions frequently impose diagnostic difficulties. There are myriads of plant-derived hepatotoxic substances which may or may not cause liver injury in individuals. The severity of liver injury depends largely on the toxicity of the substance, the amount of exposure and the individual's susceptibility. These toxic substances cause liver injury not only through the mechanism of intrinsic hepatotoxicity but also through the idiosyncrasy as in conventional drug-induced injury. Therefore, theoretically, it is possible to apply pre-existing CAMs (Causality Assessment Methods) to the assessment of causality in cases with diagnostic difficulties.