Chinese herbal medicines (CHM) and Chinese proprietary medicines (CPM) are widely used by people of Chinese origin throughout the world. Although the use of these medicinal materials rarely causes significant toxic effects, cases of severe and even fatal poisoning have occurred after medication with herbs containing aconitine, podophyllin, and anticholinergic substances. Furthermore, CHM and CPM are often adulterated with substituted herbs, heavy metals, and western medicines; such contamination can have important clinical consequences. In Hong Kong, surveillance and legislation are required to control the use of some of these herbal preparations. In other countries, medical practitioners should also be aware of the possibility that these herbal-medicine-related remedies may cause significant clinical problems in their Chinese patients.