Brominated flame retardants (BFRs) are widely used in consumer products. Their toxicological effects as endocrine disruptors have been partly examined. However, their immunological effects have not been elucidated. To evaluate the effects of BFRs on immune responses, we investigated whether BFRs affect phenotypes and the function of immune cells in vitro. Here we examined the commercial pentabromodiphenyl ether mixture (DE-71), octabromodiphenyl ether mixture (DE-79), decabromodiphenyl ether mixture (DE-83R), hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA). Splenocytes and bone marrow (BM) cells were prepared from atopic prone NC/Nga mice. Splenocytes were exposed to each BFR for 24 h. BM cells were cultured with granulocyte macrophage-colony stimulating factor (GM-CSF) for 8 days and BM-derived dendritic cells (BMDCs) were exposed to each BFR for 24 h. In another experiment, BM cells were cultured with GM-CSF in the presence of each BFR for 6 days during BMDC differentiation. After exposure, cell surface molecule expression and cytokine production were investigated. Each BFR increased MHC class II and CD86 expression and interleukin (IL)-4 production in splenocytes. DE-71, HBCD and TBBPA increased T cell receptor (TCR) expression in splenocytes. In both experiments, all BFRs except TBBPA increased DEC205 expression in BMDCs. BMDCs that differentiated in the presence of HBCD showed enhanced MHC class II, CD80, CD86 and CD11c expression. The results demonstrate that some BFRs may stimulate immune cells. BFRs can induce or enhance immune/allergic responses by increasing antigen presentation-related molecule expression and IL-4 production. Copyright © 2012 John Wiley & Sons, Ltd.