The purpose of this study was to investigate immunomodulating effects of environmental toxicants on cytokine and ROS production in white blood cells. Immunomodulating effects can either be investigated on a healthy immune system or on an immune system during the challenge of infection. To simulate infection two bacterial analogs, LPS and Pam3CSK4, and the bacteria Y.enterocolitica were used.Y.enterocolitica was used as a test candidate for the development of a whole blood model for characterization of bacteria. A concentration-dependent increase in Tnf-á production was observed after exposure to Y.enterocolitica. PBS should be used as a solvent for the bacteria, because cytokine production was induced by the growth medium (BHI). The volume of PBS (100ìL-1mL) did not seem to affect the relative Tnf-á production pr. CFU in whole blood. The Tnf-á production in whole blood was also tested after exposure to the environmental toxicants A1242, A1254, Bisphenol A, HBCD, PCB77, PCB153, TBBPA and Triclosan. The first screening showed small but significant differences between the controls and all the toxicants tested. Different concentrations of A1254, HBCD and PCB77 were investigated further; no trends were observed. Priming with the bacterial analogs LPS (1ng/mL) and Pam3CSK4 (100ng/mL) showed no immunomodulations.Induction of ROS-formation in human neutrophil granulocytes by exposure to A1254, Bisphenol A, HBCD, PCB153 and Triclosan were investigated with a luminol chemiluminescence assay. All of the toxicants, except Bisphenol A induced a concentration-dependent increase in ROS formation. Bisphenol A induced a reduction of the basal DMSO level of ROS. Immunomodulations of some of these responses were investigated with LPS priming or coexposure with 250 000 CFU Y.enterocolitica. The LPS priming seemed to suppress the normal response to the toxicants. Y.enterocolitica coexposed with PCB153 and Triclosan suppressed the effect of the single toxicants at higher concentrations, while A1254 and PMA seemed unaffected. Binary mixtures of Triclosan, HBCD or Bisphenol A with PMA or PCBs were also investigated and compared to predicted values by the Loewe or the Bliss model. Only mixtures between Triclosan and A1254 or HBCD were significantly different from DMSO. PCBs mixed with HBCD seemed to follow concentration addition, and the mixture with HBCD and Triclosan followed independent action more closely. The models predicted the combinatory effect of all the other mixtures poorly.