Recently, there has been growing interest in the use of traditional Chinese herbal therapy (TCHT) decoctions for the treatment of atopic eczema (AE). The mode of action of this treatment is still unknown, and in order to investigate this we have analysed the effect of an extract of these herbs (TCHTE) on interleukin 4 (IL-4)-induced CD23 expression on peripheral blood monocytes from non-atopic subjects. We found that TCHTE inhibited CD23 expression up to 60% (P < 0.001), whereas the placebo extract had no significant effect on CD23 expression. This inhibition was dose-dependent, and TCHTE was effective at a concentration of 250 micrograms/ml (P = 0.001). If TCHTE or placebo was added after IL-4, the action of TCHTE could still be seen at 12 h. This inhibition was not due to cell death, as peripheral blood mononuclear cells (PBMCs) cultured with TCHTE or placebo at a concentration used in these experiments had a similar viability to control cultures. Down-regulation of the low affinity receptors for IgE on antigen-presenting cells in patients with AE may contribute to the benefit observed following treatment with TCHT.