After administering standardized mistletoe extract, Viscum album L, (Iscador injections of 0.1 mg twice and 1.0 mg in defined intervals) the functional characteristics of microcirculation and immunological behavior of the white blood cells in different target tissues (derma, intestine) were investigated in healthy volunteers by vital microscopic investigation over 13 days of observation. The investigations showed a temporarily improved function of the microcirculation and an increased adhesion and transmigration of white blood cells in the target tissue areas. This observation was evaluated as a biologically relevant immunomodulation. Further investigations under pathophysiological conditions with regard to complementary administration of the test substance (e.g. to cancer patients) appear promising.