Cimicifuga racemosa (black cohosh) is commonly used in traditional medicines as treatment for menopausal symptoms and as an antiinflammatory remedy. To clarify the mechanism of action and active principle for the antiinflammatory action, the effects of aqueous C. racemosa root extracts (CRE) and its major constituents on the release of the proinflammatory cytokines IL-6, TNF-alpha, IFN-gamma, and the chemokine IL-8 were investigated in lipopolysaccharide (LPS)-stimulated whole blood of healthy volunteers. CRE (3 microg/microL and 6 microg/microL) reduced LPS-induced release of IL-6 and TNF-alpha in a concentration- and time-dependent manner and almost completely blocked release of IFN-gamma into the plasma supernatant. Except for IFN-gamma, these effects were attenuated at longer incubation periods. IL-8 secretion was stimulated by CRE. As shown by quantitative real-time RT-PCR, effects on cytokines were based on preceding changes in mRNA levels except for IL-8. According to their content in CRE, the phenolcarboxylic compounds caffeic acid, ferulic acid, and isoferulic acid, as well as the triterpene glycosides 23-epi-26-deoxyactein and cimigenol-3-O-xyloside, were tested at representative concentrations. Among these, isoferulic acid was the prominent active principle in CRE, responsible for the observed inhibition of IL-6, TNF-alpha, and IFN-gamma, but not for IL-8 stimulation. The effect of this compound may explain the antiinflammatory activities of CRE and its beneficial actions in rheumatism and other inflammatory diseases.