Viscum album (VA) preparations have been used as a complimentary therapy in cancer. In addition to their cytotoxic properties, they have also been shown to have immunomodulatory properties that facilitate tumor regression. During the tumor growth, the dendritic cells (DCs) are inactivated by the production of tumor factors such as VEGF, IL-10 and PGE2. In the present study, we examine the hypothesis that the effect of VA preparations on DCs may be one of their immune modulatory mechanisms that facilitates effective tumor regression. The CD14 +ve monocytes were isolated from healthy donors by Ficoll followed by positive isolation using magnetic beads. The day 4 old immature DCs were treated with VA Qu Spez and VA M Spez at 5 and 10 microgram/ml for 48hrs. The expression of various surface molecules was analysed by flow cytometry and the cytokine secretion by BD CBA Human Inflammation kit. The functional effect of VA Qu Spez and VA M Spez was analysed by mixed lymphocyte reaction (MLR) with allogenic CD4+ T cells. DCs treated with VA M Spez and VA Qu Spez at 10 microgram/ml displayed an increased expression of antigen presenting HLA-DR molecule and co-stimulatory CD40, CD80 and CD86 molecules accompanied with an increased IL-6, IL-8 and IL-1beta secretion. The ability of the DCs treated with VA to induce the proliferation of allogeneic CD4+ T cells further substantiates the immunostimulatory effect of these preparations. The VA preparations stimulate the expression of various molecules and cytokine secretion by the human DCs. This information should assist in understanding the immunomodulatory properties of VA preparations and improving the therapeutic strategies.