Si Wu Tang, a Chinese herbal formula composed of four Chinese herbs (Danggui, Chuanxiong, Baishao and Shudi) was analysed for its magnesium, manganese, zinc, iron and calcium concentrations when made into a decoction. The commonly prescribed amount is 42 g in a specific ratio of the four herbs, and from this it was determined that all metals analysed were within safe limits and daily tolerable limits would not be able to be reached by ingesting this formula (42 g/day) alone. The highest metal in the Si Wu Tang decoction was found to be magnesium at 25 mg/L, which is under the daily intake recommendations. Varying the brewing time during the preparation of the herbs was found to have various effects on the different micronutrients when made up into separate decoctions from 1 g of each separate herb and these observations may be beneficial to Chinese medicine practitioners who wish to vary the Si Wu Tang formula to better suit a patient's needs. Samples were analysed at least in triplicate and error was found not to be over 15% at the 95% confidence level. Investigating the amount of metals present will increase the understanding of the levels of these beneficial metals and the potential curative effects they provide. [ABSTRACT FROM AUTHOR]