Traditional Chinese medicine (TCM) has recently yielded a number of chemical compounds with clinically significant anticancer activity. The theory of TCM formulas, however, unlike Western medicine, is based on the interactions of the various Chinese medicinal materials in the body, rather than the activity of a single purified chemical compound. Mechanisms for the possible synergistic anticancer effects of components in TCM formulas have recently been postulated. Advanced research on the clinical effects of TCM formulas, however, has been hampered by inconsistent dosage formulations and unreliable quality control. Scientific challenges in dosage formulation and methods for ensuring quality control of TCM products will be discussed.