The present study was designed in order to evaluate the effects of five homoeopathic complex preparations on functional activity natural killer cells (NKCs) in advanced cancer patients. We examined the effects of Coenzyme CompositumW, Ubichinon CompositumW, Glyoxal CompositumW, KatalysatorenW and TraumeelW on the functional activity of NKCs. Experimental procedures included in vitro and in vivo trials. The in vitro trials were performed in NKCs isolated from 12 healthy volunteers (aged 44 ` 4 years) and incubated with the five homoeo- pathic complex preparations. The in vivo trials were performed in 15 advanced cancer patients (aged 55`12years) supplemented for 3months with the homoeopathic preparations. All five homoeopathic preparations significantly increased the cytotoxic activity of the NKCs at the lowest NKCs/target cell ratio 12:1 (p < 0 05). The order of activity was: Ubichinon CompositumW > Glyoxal CompositumW > KatalysatorenW>TraumeelW>Coenzyme CompositumW. In the advanced cancer patients, the homoeopathic preparation significantly increased NKCs cytotoxic activity (p < 0 05). The homoeopathic complex preparations tested in this study can be used as an adjuvant immunotherapy in advanced cancer patients.