By means of a bioassay-oriented fractionation of the CO2 extract of Calendula flowers, the triterpenoids are shown as the most important anti-inflammatory principles of the drug. Among them, the faradiol monoester appears to be the most relevant principle for the activity of the drug, due to its quantitative prevalence. The unesterified faradiol, not present in the extract, is the most active of the tested compounds and equals indomethacin in activity, whereas the monools psi-taraxasterol, lupeol, taraxasterol, and beta-amyrin are less active than the free diol. The anti-inflammatory activity of different CO2 extracts is proportional to their content of faradiol monoester, which can be taken as a suitable parameter for the quality control of Calendula preparations.